An argument could be made that she emotional cheated on her boyfriend (really dude? You were talking about the things you wanted to do to each other. Who the fuck does that as regular banter with a coworker? C'mon. You wanted her so bad that you didn't care she had a boyfriend because she told you she had 'emotionally checked out' and was in it for 'the lease'. Are you trying to convince reddit of that or yourself?). Be better than that. Don't entangle yourself with people who are already in relationships. Couples break up and figure out shared leases all of the time. If she's even to be believed...

Distance yourself from her. Cut the 'friendly banter'. Be better. Next time you have a crush on someone in a relationship, make the choice to cut that shit off.

Quite a big coincidence that she asked you about the sexual tension between you, conveniently broke up, fucked you, then had to get back home...