Need some advice please

I made a post a few weeks ago about losing my son at 16 weeks pregnant. Prior to that my ex(child's father) and I broke up in October and we didn't speak for months. By the time he came back around Christmas I had already lost our child. Well we started hanging out daily for about a week now. I knew we wasn't getting back together even though I had these feelings still that he knew about. I mean I never got to heal because I was alone missing him and now I'm still grieving over our son so being around him was good for me. The first night I went to hang out with him he asked me to just stay the night ,I did and we ended up sleeping together many times that night,next night had sex again which he initiated all time.The next night the sex got really passionate and I stopped it but try to pursue it again and he rejected me. I left and went back to his house yesterday , when he tells me he's been talking to another girl . This hurt me bad 😞 maybe because I hoped it would work with us, maybe because we just lost a child and it's been a month , or maybe the fact he was sleeping with me while he was talking to this girl. It just didn't sit right with me last night being told this, it broke my heart all over. I just enjoyed being able to be around him again and possibly rekindle things. I couldn't speak I had a lump in my throat that wouldn't go away and just had to stop myself from crying. He said he wants to continue hanging out and possibly have sex with me and he doesn't have to tell her. That didn't sit well with me either because it's not fair to me knowing the truth and her being led on like that. I had to tell him last night was the last time he'll see or hear from me. I know there are many possibilities it could be I'm just lost and . I know he still loves me , he tells me and says I'm the best he's ever had in every way but goes and tries to have his cake and eat it too. I'm hurt. Y'all, how and what can I do to start to heal.