Me and my baby daddy still have feelings for one another but cannot be together.

This is a long story (5 years worth) so I’m going to shorten it. A couple years into our relationship he started going out all the time, I’d be waiting around for him, he’d go meet other girls with his friends and I once found messages between him and his best friend saying “if I don’t get a shag of one of these girls I’ll just go ambers and get 1”. We fought like crazy, it was toxic and we constantly tried to get one up on one another. Eventually just before I caught pregnant I ended it with him and thought if I moved on straight away I’d be over him... pathetic thought. But actually when this lad I only knew for about a week tried it on with me, I kissed him back but it made me feeling disgusting. I can’t say we had sexual because we never because I started crying in the middle of it because I realised I wanted my ex/now my baby dad. I told him everything and I needed him so to “fix me”? I ended up catching pregnant, we got back together but after that he hated me which is understandable, I hated myself too. He was forever saying our baby wasn’t his, he wished me dead, his family were awful to me, they then said I was faking it. I ended up really ill in my pregnancy. I had him via c-section and after 1 hectic year of him not seeing him, then he was for many reasons, sleeping together when he was first born etc I realised this wasn’t fair my son. There’s a lot more into it... his family hate me, they got people watching me and write stuff on social media, his own man (baby dads mum) never brought her 1st born grandson anything for his first birthday because at the time they had no contact. They weren’t allowed contact because of how mentally abusive he was and once physically. I have him a 4 months break if being blocked, no contact between any friends or family. We rectory got back into contact and his begging to see his son. I believe he should so we have agreed to not get family’s involved because they hate one another but just me, him and our son meet at a play area. He can go off and play with our son, be in charge and I will still back and mind my own business, I’ll probably take course work or something like that.... however there’s one main problem. This has to be about our son, he cannot grow up around this, it is not right and I refuse to mess his life up because of mine and his father being immature etc. His dad in them for months slept with another girl and that’s the cut of for me. Some people can go back with someone who has slept with somebody else and each to there own but me... i cannot. But I know I love him but I won’t show him that, his told me he loves me, his actually a little obsessed but then he turns and says that he hates me etc. So my main reason is I need some help/advice about how I go about being around him, how I don’t seem flirty because I think I am but don’t realise that because I know deep down that ever chance of us both changing and growing together and having that family is gone. I know he loves me and I know I love him, I constantly think about him and I’m lonely but for my child’s sake I won’t go back there but that doesn’t help how hard it is. How do I move on? How do I be strong enough to hold back and how do I not fall back into that toxic trap again. I don’t want to play games if he can’t see our son and then he can. I want him to have a relationship with his son so eventually he can have him by himself (he can’t at the moment because of the time a part our son doesn’t remember him and I wouldn’t feel right just leaving my son with him).