In some ways, Sasuke was the glue holding the team together, which is the reason that the team fell apart after Sasuke's desertion; each member of Team 7 went their own way and did their own thing without him there. Even when the team reassembles, the unity between them centers on Sasuke, since a major reason for Naruto and Sakura's closeness in Part II is based in their shared dream of saving Sasuke and their mutual friendship to their absentee Uchiha teammate. Sasuke is the primary reason that Naruto and Sakura are even friends to begin with, seeing as how Sakura was unwilling to empathize with Naruto or even treat him well until Sasuke influenced her to start trying to be kinder to Naruto.

When Sasuke decides to share his lunch with Naruto, Sasuke marks himself as Team 7's unofficial leader, leading and guiding his team through example and protecting them throughout the duration of Team 7's partnership. Sasuke operated as leader of the genin trio, and as such, the responsibility and burden of protecting his team felt on his shoulders in a way that it never does for his teammates until Sasuke desserts, which roughly forced Naruto into the role that Sasuke had previously always filled and Naruto had to grapple with the burden of leadership suddenly thrust upon him.

Being unofficial team leader without adequate emotional support from the other three team members is one reason factoring into Sasuke's desertion. Sasuke was pushed into being responsible for the team at a young age when he wasn't yet ready to assume the role. Having his comrades depending on him constantly while Sasuke was rarely allowed to depend on them weighed too heavily on Sasuke and eventually became a crushing weight he crumbled under.

Sasuke is held to higher standards than the rest of the team; he's expected to be flawless and perfect, whereas Naruto and Sakura are given more leeway and room for making mistakes. Sasuke doesn't just have to look out for himself, Sasuke has to look out for his two teammates. If Sasuke freezes up, his team dies.

If Naruto and Sakura freeze up, Sasuke is supposed to have their back. Sometimes it's due to Kakashi being absent from their missions, but sometimes even when Kakashi is there, Sasuke is the one to have to step up as leader.

It fell upon Sasuke's shoulders to protect for and provide for his team, crushing pressure to perform well that Naruto and Sakura didn't have to deal with. This created an unbalanced and unfair distribution of responsibility on the team. Naruto and Sakura got to experience the carefree aspect of being part of a team whereas Sasuke was conditioned and expected to be responsible for his two weaker comrades and carry the team whenever necessary. Though don't get me wrong: Sasuke had plenty of carefree and fun days with his comrades too, it's just that the tense moments tended to be more tense for him than the others because not only was he having to protect himself, he was also having to make sure that Naruto and Sakura were safe and protected as well.

Though of course Naruto and Sakura both saved Sasuke from some near-lethal scenarios on multiple occasions, so it's not an entirely one-sided deal, and I don't want to downplay Naruto and Sakura's helpful contributions. I simply want to emphasize that the burden of responsibility fell hardest on Sasuke's shoulders and was a heavy burden for him to bear alone (the role of leader is nearly always a lonely one), whereas Naruto and Sakura didn't have to worry about the team's welfare as much because Sasuke was doing that for them.

Sasuke is a role model for both Naruto and Sakura: he's the person they admire most and are inspired by. Sasuke's role is the protector and provider role, making him sort of like the head of the family that is the Team 7 trio.

Naruto and Sasuke have a distinctive little brother/big brother relationship, with Sasuke as the protective older brother. On multiple occasions we see Sasuke leap to defend Naruto, even when Naruto is careless and thoughtless in regards to his own safety. We see that protectiveness during the ninja ambush in the Land of Waves when Sasuke bravely protects his team; meanwhile, Naruto freezes up in fear:

Sasuke proved he was willing to die to save Naruto's life in the battle against Haku:

And before that sacrifice, Sasuke was looking out for Naruto, pushing him out the way and even carrying Naruto to prevent his teammate from being shredded to ribbons.

Sasuke was willing to die for Naruto and Sakura to buy them some time to get away from Gaara:

When Naruto is angered by the unfair mistreatment that Gaara has to deal with and rushes to aid the Sand jinchuriki, Naruto turns his back on the enemy forces with foolish disregard for his own safely. It is Sasuke, ever watchful, who covers Naruto's wildly unpredictable behavior without hesitation, reflexively defending Naruto from the enemy's kunai when Naruto is too careless and reckless to pay attention to such attacks. I might add that Kakashi was standing right there when this occurred, but it was Sasuke who stepped in to protect Naruto, not Naruto's sensei.

In Ninja Clash in the Land of Snow, when Team 7 is attacked by a barrage of kunai, Sasuke warns Kakashi, "careful!" before himself leaping out of the line of fire (notably, Kakashi doesn't shout any warning to his teammates at all).

Immediately after Sasuke had gotten himself to safety, his instant concern is to check on his team and take stock of his teammate's positions, as he immediately asks Sakura "where's Naruto?" Sasuke was the first one to notice, and the only one apparently paying attention to his teammates' status and locations. Again, another moment showing how Sasuke is looking out for his entire team, aware of his surroundings and checking where his teammates are at and what their state is, even before Kakashi is.

Or how about when Naruto was about to plunge off a large waterfall? Kakashi was present, lounging on the river's edge while his three teammates were hard at work on their mission. Yet when Naruto gets carried away by the rushing water and is about to plunge over the waterfall's edge, it's not Kakashi who jumps to rescue his student, it was Sasuke who was watching Naruto and didn't waste any time in rushing to assist Naruto.

Not to mention how frantic Sasuke was to protect Naruto from Itachi after Sasuke learned his older brother was targeting Naruto. Sasuke didn't hesitate a moment before feverishly searching the streets for Naruto, not resting until he'd found his Uzumaki comrade. Sasuke ran all the way to a nearby town, presumably running at full speed a decent distance, showing how determined Sasuke is to protect his teammates.

Sasuke isn't invested in teamwork for only on the mission or on the battlefield, Sasuke takes teamwork seriously during off-days and downtime too, sweeping in to rescue his team even when he's seemingly not around. We see that in the Fourth Hokage's legacy episodes when he stops the Rain ninja from washing his friends away or when the Sand Ninja are messing with Naruto and Sakura, Sasuke suavely steps in to stop Kankuro from beating up Naruto.

Rather than sit back and watch the spat between Naruto and Kankuro play out from a safe distance or turn a blind eye to avoid getting involved in Naruto's problems, Sasuke gets involved and interferes, intercepting on his team's behalf and using his authoritative presence to stop Kankuro picking on Naruto and Konohamaru and crew.

It's possible that Kankuro, Naruto, and Konohamaru just happened to conveniently pass under the tree that Sasuke was presently occupying. Although it seems just as likely that Sasuke caught sight of the incident and chose to position himself in the tree to make his involvement look cool and nonchalant, perching in the tree from which he chose to get involved. It wouldn't be the first time Sasuke used physical positioning to his advantage and to make a statement. Fans can interpret it either way, but what is clear is that when his team is in danger or needs help, Sasuke is quick to come to his team's defense and Sasuke takes his affiliation to his team seriously.

The Forest of Death arc is another incident emphasizing Sasuke as leader: Sasuke isn't just his team's protector, but also his team's planner and provider, as Sasuke is frequently expected to strategize, plan, and problem-solve. Sasuke has to be the one to strategize and cannily look out for his teammates, who are heavily reliant on Sasuke's help and protection.

Sasuke concocts plans and strategies to keep the team safe (such as coming up with the idea to use a secret code as a safety precaution or his planning session with Sakura), is the most aware and watchful of his team (as proven when he realizes that "Naruto" is an enemy imposter, something Sakura carelessly overlooked), or how he is protecting the team (he has to save Sakura multiple times), he keeps secrets from Naruto so as to not worry the team (refusing to inform Naruto about the curse mark in order to keep team performance up), and he provides for the team (challenging Kabuto for his scroll).

The English dub version of the anime directly underlines Sasuke's exasperation and exhaustion with always having his team so dependent on him, as when he is fishing and helping gather food for the team, Sakura asks Sasuke to start the team's campfire, to which Sasuke sighs, "I've gotta do everything around here" (though it should be noted that the manga and sub translations are quite different – and presumably more accurate - on this line). 

Moreover, as soon as Sasuke leaves Naruto and Sakura for the brief errand of refilling their canteen (another responsible task), he can barely leave the pair unauthorized for more than a few minutes without them trying to cheat and ruining the exams for the team (thanks to Kabuto's interference, Team 7 didn't lose the entire exams while their leader was going for a few minutes).

Sasuke challenged Kabuto to a fight for the Heaven scroll, an instance of providing for his team. If Sasuke fights Kabuto alone, it's a chance to gain the Heaven scroll without dragging Naruto and Sakura into the conflict, allowing the whole team to benefit without Naruto and Sakura having to do anything. Sasuke takes that burden upon himself, assuming responsibility for the team's success.

Sasuke praises his teammates for their contributions as well, but like a leader, he's willing to take on the most difficult challenges himself, even when he's seriously injured or at a great disadvantage. In both the fight with Haku and the fight against the Rain ninja trio, Sasuke openly praises Naruto for his contributions, but also tell Naruto when he's done enough or that he can take a break.

Sasuke is watchful not just of his team's safety but of their stamina and endurance as well. Sasuke doesn't ask his teammates to push themselves too hard. Rather, Sasuke is considerate of his team, praising their hard work and their skill, and also encouraging them to take things in moderation and at their own pace, ironically despite the fact that Sasuke is always pushing himself too hard and would never allow that kind of leniency on himself (something even Sakura notes about her husband in Boruto).

This is leadership behavior: Sasuke leads by example, is considerate of his "subordinates", and only asks that they do whatever they can within their power but