heartbroken 😞💔

I gave birth 6 weeks ago to the most precious little boy. Two days ago I went on my first night out since having him. I did a BBQ then we went to hit the town. My boyfriend brought 3 of his friends and I brought my best friend. He left us all night he gave me attitude he clearly didn't want me around so my night was ruined and he went home without us, I left my phone at home I had no money and it's a 50 minute drive away so I had to get a taxi and pay when I got home. The next day he was very distant and he tried to hide it but he then told me he shoved his tongue down two girls throats that night. First of all I was in the same club he was avoiding me all night and I didn't do anything to make him be like that towards me. I have my figure back in fact I look better than ever I'm back down to a size 8. He said he was kissing one girl on the dance floor then he was afraid incase I caught him so he took her in by the toilets then continued to kiss her. I then walked right by them and didn't even see them, he opened his eyes and saw me and stopped straight. He then went onto the dance floor started dancing with another girl and started kissing her too. He told me that he's always wanted to try it with other girls because I'm the only one he's been with, so he took her to the toilets to try and do sexual things with her but I walked past. He continued to tell me he didn't care about me that night he didn't know why. He said he wanted the freedom his friends had but he didn't want to end things because we are a family. We have a 6 week old little boy and I'm afraid I can't do it on my own. He has bad reflux and it's a struggle for both of us to look after him. He is deeply sorry he's poured his heart out but that doesn't take back what he did. I have not eaten or slept in 3 days my stomach is in knots I can't stop crying because he's messed everything up. I love him to pieces we have been together for 5 years and I'm so torn. I know the best thing to do is leave him and I have ended everything he's sleeping on the couch and I hate his guts. I don't want my little boy to grow up without his daddy around because he is an amazing dad. I'm so afraid of being alone I have terrible anxiety and postnatal depression how am I going to get over this? I rally want to try and put it past us and move on but I just can't stop thinking about it. And what makes it worse that girl didn't even have much going for her and she looked in her 40's we are both 21. Has anyone's partners ever cheated on them and how did you manage to put it behind you?