Help need advice !! 😭 girls !!! Boyfriend did something and he reacted stupid and didn’t want to say

So March 26 I had a baby and when he was 2 weeks old my boyfriend went out to his friends party and I told him not to go I never did anything to him I trusted him to go but it’s been 3 months after that party he started acting distant and he started accusing me of cheating started to have stress and tell me stupid things stop talk to guys and he went into a mental home so I guess that scared the shit outta him he let it out saying he cheated on me by making out with a girl idk what to do like how do I know if it was more than just a make out we’ve dated for 5 years then had a baby I feel so low self esteem confidence because I just had a baby and my body doesn’t look great I weight 136.6