How to let go?

I’ve known my child’s father since we were kids. He was one of my best friends. We watched each other literally grow into adults. After chasing after me for months, I reluctantly gave him a chance & we started dating when I turned 18. A year after, I got pregnant. I thought this was the man of my dreams like I had hit the jackpot. But a few months ago, my perfect family dissolved when I found out he was cheating on me. He was on various dating sites and slept with a few girls. I feel so lost and like I was deceived. I’m 22 but I feel like a scared little girl who needs her mother. I feel like I’m still in a state of shock. I stay strong because of our child but I can’t help miss him and hope it’s all just one fucked up dream. I dig my head in work and do OT constantly because it keeps me distracted but once I get home, a wave of sadness overpowers me. It feels 10x worse when my toddler hits a new milestone cause I experience it all on my own. There’s times I forget we’re not together anymore. When something funny or crazy happens, my reaction is to call him and tell him all about it and then reality comes crashing down. Idk how to let go of the family I thought I’d have. It’s hard to hate him because how can I hate someone I never really knew..? & Having to coparent only makes things difficult and confusing for me. I just want to be happy again. How long did it take for you to let go? What helped you?