Four months

It has been four months since my son has seen his Daddy. His Dad was always in and out of his life, but after he got his new girlfriend pregnant and had their son together he completely quit coming around and acknowledging us.. He didn’t even come to our sons 2nd birthday party last month, or tried seeing him period. He even lied about being in a terrible car accident so he wouldn’t have to come see our son (i know it was a lie because his best friend told me) I just wish I understood why he could be this way, his other son was born a week and a half after our sons 2nd birthday and so far has been there for him, but why not his first baby? Our son did nothing to deserve this. I just wish I had answers...