Coping with cheating spouse, divorce and new baby

I am currently in a divorce with a military man who cheated on me with another solidar while i was 5 months pregnant. My son is now 2 months old and hes never came to see him, sends no money and pretty much wants nothing to do with him. Im his 2nd wife and have his 2nd child. The other day I went to lunch with his dad and step mom who are very upset with him and the dropped a bombshell saying that hes getting remarried in April and she is now pregnant. I can get over the cheating and move on but what do I say to my lil man, how am I going to explain to him when hes older why his daddy was not there for him but there for his other kids, what if i dont find someone thats good enough for my son. We are currently going back and forth with the divorce lawyers and he agreed to give me sole custody but only wants to pay 279 and my lawyer was like Oh no, she wants him to pay 776 based on his incom, health insurance and his prior child that he pays 250 for, Im sure she will win cause shes awesome, and his lawyers and idiot (he made 8 mistakes in the divorce papers, includeing the fact that he put his first wifes car into his current divorce papers and i dont have a car) I mean the money eases the financial part, but what about my son? He says hes sooo happy with his new girl and shes his bestfriend and hes gonna be a daddy but what about Mason? and his first daughter that he barely sees? I just dont think its fair and I dont know how to act? What can I tell him when hes older, I dont want it to seem like im keeping him away.... although thats a good idea sinces hes has temper problems, puts his children last and has pror drug issues. Im just venting but can anyone ease my mind if they went through something similar

By no means is this all his fault, i didnt know he was like this he said his firts wife cheated on him, and i only knew him for 6 monthes before we married an moved to germany, so i do take blame for that part, and i didnt know he was cheating cause he was out on missions an lied and said his unit was majority males and he called me every single day