What to tell her?

I consider myself bisexual and I'm engaged to a male. I am friends with a girl in school who is also attracted to men and women and we do a bit of flirting. I've never flat out told her my preference but have hinted at it. She has spent the night over my place a few times with simple plutonic cuddling, (which the fiancé is aware of) but a couple days ago the cuddling turned into some "heavy petting." We never talked about it and went on like nothing happened, but I sense things feel different.

I don't know if I should bring it up and what to say? I don't know what I expected from this relationship because I do love my fiancé, but I don't want her to feel like I'm pulling her along. I do find myself attracted to her and don't want to stop hanging out with her but should I tell her how I feel about her knowing it can't go anywhere? Or wait and let her come to me? I also don't want her to think I do this sort of thing all the time. My last relationship with a female was about 8 years ago.

Thanks for the advice!