break up advice?

Probably gonna sound silly. But, how do you get over a break up? He was my first and only boyfriend of 3 years. We have a 6 month old son together.  I honestly don't know how to move on.  He was my best friend and first love and I just cannot let go. 😞 I'm stuck in the trap of needing someone to talk to but he was the only person I talked to most days. I've never felt this broken. I'm 22 btw, I feel like I'm too old to feel this stuck. 
Also very self conscious after having our son. I lost all of the baby weight but can't get rid of the belly flab since I had a c section. I honestly feel so washed up. This part of the reason I'm so hurt. He cheats when I'm already feeling so drained and down about myself. I know it'll get better and someday I'll look back and laugh. But today I can't stop crying.