How to get over Cheating...

Not to long ago I posted a topic about my boyfriend/father of my child cheating on me. I found a picture of them together but all other information is just vague. I look at this picture of them everyday and wonder where I went wrong. I cry daily knowing he'd rather be with her than with his own child. How can I get over this? I was with him for three years and did everything for him, paid bills, or gas, bought him whatever he wanted, let him have sex even if I didn't want to, I never told him no, and he still cheated. I see a therapist and all she did was show me how the grief process works. He didn't sign the child's birth certificate, he doesn't pay child support, and he said he would refuse to pay child support and would never go to jail over our child. Nothing gets my mind off of this, I just constantly think of all the things they do together, the things I should be doing with him. I keep contacting him, even though I know he doesn't care. He's only seen our child 2 times in 6 months. My parents told me if he fights for custody he will win because I keep contacting him but I can't stop. Idk what to do, I feel like I'm loosing my mind.