So this is going to be a very messy situation.
I have a family friend who I've had a decent bond with since childhood. We both used to hang out a lot and developed feelings for each other and there was a lot of tension from the start, however we never confessed. Then we grew up and parted ways but still were in contact. Fast forward to now, she has a boyfriend of 4 years and is in a long-distance. I was single at the time and had to move back to my hometown. Our houses were adjacent to each other so there was a lot of hanging out. I kept falling for her and eventually decided to confess, and got rejected at first. I was devastated because I was at a very low point in my life also back then and I just limited my contact to move on. But one day, there was an opportunity, (which is a story in itself,) and we kissed. Eventually, we used to make out a lot and kind of got into this relationship that we haven't named yet. From there, it led to sex. However, I got way too attached emotionally now and even she says she is.
The problem is that I have become too insecure in this relationship. Because she is obviously not ready to leave her boyfriend (who is probably better than me) and says she just can't but she doesn't want to leave me or lose me at all because of the bond we have. If we end things, it's just not possible for us to be in contact and I cannot afford that. But whenever I think of her with her boyfriend, it hurts. I know I shouldn't have gotten into this relationship at all because she is cheating and is not sure of me, but I just cannot leave anymore. It's hurting me a lot. I have become way too insecure which has led to a lot of fights. We have also broken up a couple of times but she always comes back. I don't know what to do anymore.