How do you leave someone?

Hi so this might be a long post so bare with me. So my boyfriend and have been together for almost 6 yrs. we have a 2 year old together. And in the begging of the relationship he cheated on me and “got the other women pregnant” we asked for a test and she disappeared. So after I gave in and forgave him a few weeks later he had other women on his snap chat talkin about “oh I’ve always loved you” then when confronted he said that’s his homeboys sister like What?? Anyway this was like 2 years into our relationship but now that we have a kid and been together this long he’s changed but now I just don’t feel it. We barely have sex. I can’t stand when he touches me and he asks why and I just tell him idk?? And if we do have sex it’s like once every other month. Like I don’t feel like I’m in love with him anymore and when I try to talk about how I’m not happy he flips it and changes it to him and maybe he should just leave. But like why can’t you be a civil adult and talk about our feelings and validating them. He adds random women on his Snapchat and deletes the conversations so I felt hmm 2 can play that game. But at the same time I don’t want my child to have to go through that trauma of both parents only staying because of her. When I’m more then willing to co parent but apparently that’s not what happens he thinks if we break up she doesn’t have a father anymore. ANYWAY. So my question is. How do you leave someone who’s changed for you (sorta) and thinks the relationship is going good. But you’re secretly not in love with them anymore.