Made friends with a girl at college. Asked her out, she said she had a boyfriend but still really wanted to be friends, that's cool. She sent me a (probably) drunk text one night, I responded, and now she hasn't talked to me at all and changed her Facebook so it's clear she's in a relationship.
Did I fuck up? Should I leave it alone? It's been 4 days, maybe she's just busy and I'm overthinking it.
Depends on what she texted you and what you replied with.
Yes you should leave it alone. She's in a relationship and texting when drunk then not responding to you is an asshole thing to do.
Make new friends and don't bother with her.