My ex

My ex and I broke up almost a year ago. Long story short we’ve been in contact since then I’ve denied having sex with him because he has a gf. As of August I told him yes and we’ve been having sex. He said he’s tried getting over me while with her he still has feelings he regrets hurting me... as of early November I told his mom and gf what he was doing with me and well idk what to do. I know he has feelings for me and it’s not just sex. Though most days it is. My roommate says we are low key dating and honestly I have always had feelings I dated and have tried moving on but I can’t. His gf knows what he did and is with her I want to tell him me or her, but ik it won’t be me.... I don’t want to lose him again and well he came looking for me after not talking to me for months. What should I do. I’m tired of being the the other woman but I don’t want to lose him. He said I had one last chance or he was done.... done with what? We aren’t even dating.