How do you handle having a child with your best friend?

I have a month old son with my best friend of 13 years .. I am 30 divorced and NEVER wanted this to happen. We have always been able to talk about anything with each other but I am Absolutely lost for words in this situation, a better word is denial. We could never be a couple and I had a VERY hard time during my pregnancy accepting that it happened and raising another child from a another broken home and he fells the same. He has full custody of his daughter but has completely backed away from our son. I am not one of those women that trayssto make a man do right, believe people show how they really feel by their actions not by being told what to do and we are all accountable for our own doings. Not no one else's judgment. But this is totally confusing! How do you ask someone are you gonna take care of your kid or not! Any suggestions?