Is there a tag for that or something?

No. Sounds a little too long winded for a tag, personally.
Also, pretty sure this is more a topic for the official tagging thread.

Hmm, closest I can think of is the "betrayal" tag, but that encompasses multiple kinds of betrayal. Might be worth looking through those posts.
For mind-controlling someone into loving in general, there's "love" and "love_potion".
A related concept may be "netorare", where a person uses mind control to make a person cheat on a significant other.
That's the best I can do. I hope you can find something similar to what you want.

Netorare is the most accurate with that i think

I know it's not what you're looking for, because the targets are kinda fugly men, but this was a major plot point in the Once Upon a Time spinoff, Wonderland.

Jafar was the bastard son of the sultan that was rejected, so he sought to change the rules of magic to force people to fall in love so the Sultan would finally accept him.

Near the end of the season, it works, and the sultan treats him like a loving father. Jafar shanks him, because what he really wanted was for the sultan to feel the pain of being betrayed and killed by someone they truly loved.

What a weirdass franchise that entire thing was.

A post? I don't know.
A route in the game Saimin Enbu? Yes.

A good couple of the Penlight endings have the protag brainwash Hiroko, only to get cold feet when he realizes how far he twisted her original personality, and runs off in shame instead of undoing it. It's a brief scene, in a game, not a post, but pretty much the kind of thing you are looking for.