I just don't know what do to anymore 😞

SORRY LONG STORY- 
So I've been with my partner for 3 years now we have a 20month old son. I love him with all my heart and actually feel like I love him way more than he loves me. 
I feel like we have completely different/separate lives. I'm a stay at home mom while he works. I live on my own with my son and he lives with his dad he's 25 and I'm 21. I'm not happy living separate I just don't understand it there's not reason why he couldn't be here with us. It kills me. 
Lately he's been getting back involved with all his old friends, going to boxing doing boxing matches, going to football and now has joined the gym .. He works full time and does all this after work. He comes round my house at about 7.30-8 on a night and sometimes stays the night and goes at 5am in the morning . Sometimes he doesn't bother seeing us at all. I feel like there's no time for me and my son what so ever. We are the last option because he knows we are going to be here still kind of thing. 
Lately our sex life has gone down the drain also, it used to be grate but lately it's maybe once a week if that.. But it's always when he wants it, if I'm feeling it and start getting abit touchy feely he says 'it's asleep - to tired sorry' ? Like what the eff!! He also started touching me the other night and then stopped to look at his phone 🙄 I was mortified I feel so little. Like I don't exist . 
I feel like I just try my hardest to make a effort and I get it in the neck - he tells me he's 'too busy' or he needs to train harder. Even when he comes round he's so distant he's always on his for 24:7 all the time . He hardly talks me just sits and stares into his phone screen. 
About 4 months ago I got told he cheated, he denyed obviously, but the girl told me. Said he ' held her all night after fucking her ' 
I still to this day believe it happened and he knows I don't believe him  but wanted to make it work because I love him and trust me he never got off lightly -  it gets me because he doesn't even to that to me. He doesn't do anything .. I feel so disconnected. 
I want to make him see, but how 😔😭
Why can't he be here with us like a family we should be ? Just coming home to us every night would make my day - obviously we just not what he wantsÂ