So I have this problem.
I get really, really attached to people all of a sudden. It's usually after sleeping with them, which I guess is kind of normal, but it's like a flip is switched and the other person usually doesn't understand why I feel so strongly all of a sudden.

Here's my situation:
I met a girl off of tinder about a year and a half ago. We established that we only wanted casual stuff, because she had a boyfriend of a few years (who knew about this and was ok with it). I'm also a girl, btw. She wanted to experiment with another woman because she thought she was bisexual etc. It was all fine and we hooked up a few times and then lost contact for six months.

A few months ago she texted me and we ended up hanging out, just as friends this time. She had broken up with her long term boyfriend and was casually seeing someone else. After about a month or two of us hanging out as friends again, she suddenly broke up with the guy she'd been seeing and we slept together again. Now the trouble starts. I had told her that I wasn’t interested in a relationship with anyone, but then I began catching feelings for her. We started texting and snap chatting every day, a lot of times all day. I left for a vacation after sleeping with her again, and we were in constant contact the whole time.

Then when I got back, she became distant. I realized (through social media and stuff) that she'd gotten back together with the guy. I asked to hang out a few times(as friends), and she agreed but then bailed. I got the hint and we kinda fell out of touch. A few weeks ago, she asked to hang out and ever since then, we've been in constant contact again via texting and snapchat, but I still feel like she's keeping me at an arms distance. She frequently flirts with me and calls me beautiful/funny/etc, more than I flirt with her actually because I feel like I need to respect the boyfriend boundary. I’m just not sure what to do at this point.

The guy she’s seeing is head over heels for her and is a great person. He constantly showers her with gifts and goes out of his way for her. She has expressed that she feels overwhelmed by all this and doesn’t seem to feel as strongly about him. I have a hunch that she knows what an incredible guy he is and doesn’t want to leave him for that reason and for all the things he does for her, but isn’t really that…into him. However, this is just my impression; it might be wishful thinking. I’m also wondering if she’s apprehensive because I’m another woman. She said that she knows now that she’s definitely bisexual, but still.
Sorry that was so long, any advice would be really appreciated. I’m just so confused and upset over this.

TDLR: As soon as I caught feelings for a girl, she got into another relationship, but she still constantly flirts with me. I’m not sure what to do.