How do I fight this? 😭

Hi glow fam, I’m struggling so much from a broken down heart. I have a beautiful 8 month old baby boy, and for the past three months the baby daddy who used to be my boyfriend, has treated us like DIRT. He doesn’t help me support our baby physically or financially,( never has) he never stops over to see him or asks how he is, he has a new girlfriend now and is telling everyone that it’s not his baby, including her, and she believes him. It’s completely his baby. They even look so much alike.... he’s blocked me off of everything, social media, iMessage.... it hurts so bad. I never did anything wrong to him, our relationship was toxic but I tried to stick it out knowing that we were gonna have a baby... he’s acting like my son and I don’t exist and he strictly doesn’t care. I’ve never met anyone more heartless in my life. Has anyone been through a similar situation? How can I help the pain not to be so strong and move forward from this??