(This won't be your typical yandere. She's not violent and batshit insne.)

After winning the seventh gym, my team and especially your shiny Gardevoir, were treated to a really good dinner and a few days off training. This is my way of saying thank you to my team and myself.
Over around a day ago, I noticed Gardevoir has been starring at me for uncomfortable amounts of time every day. I should ask her what's up privately.

While my team was busy talking amongst themselves I pulled Gardevoir aside to speak with her.

"You've been acting really weird. What's going on?" You ask her

"I love you" she replied immediately and without a stutter.

"....Oh, but I-" you were cut off by her holding a finger to your mouth.

"I know. Humans and Pokémon having anything further than platonic relationship, or family is taboo, but I don't care. You're mine and mine alone. If you talk to any female outside of our family, I will drive them away with increasingly dangerous tactics. Understood?" She warns.

"...Yes" you answered.

She smiles a little and kisses you on the lips.
You didn't take her warning too seriously though. A month or so later you were flirting with a girl you liked. Gardevoir, clearly not liking it, hugged your arm and nuzzled your shoulder. She then gave the human woman you were flirting with Evil Eye. The woman froze in fear and Gardevoir dragged you back to the house with the rest of your pokemon.

"What did I tell you around a month ago?" She asked. Eyes glowing red.

"I'm sorry. I didn't take you seriously" you were a little scared.

"Sigh. Just don't do it again. Alright? Remember. You belong to me". She hissed a little.

A/N
I'm very sorry for this being short. I wanted to get this out, but still have it good enough to not be just slapped together in half an hour.