Sorry for the long text
I met a girl at the beginning of September this year.
I've already slept with her twice (but I didn't try to do anything else than caress her hair, we were both drunk, I even caressed her lower abdomen for a few minutes).
I already took her by her shoulders while she was with her friends that I didn't know, she let me do it.
I've already done 2-3 outings in cafes with her, which she seemed to really enjoy.
She frequently laughs at my remarks and jokes, as well as my sarcasm.
The last time I saw her, she stroked my hair several times (a good 30 seconds each time) without asking me.
A mutual friend of ours has already sent me screenshots of her telling him that she thinks I'm very handsome and cute, virile and smart, she also said it in front of me shortly after.

I don't know how to get out of it successfully, I really like her.
The problem is that she's already been in a relationship for three years with a possessive and notoriously manipulative guy (he's still on a college trip until the end of June). I feel like she is a victim of Stockholm syndrome and doesn't want to realize it.

What the hell am I supposed to do?
t. 1.85m, 23yo, solid frame and 90kg max rep on bench press
she's half-korean btw, a real qt3.14