Seriously need opinions.

When I first found out I was pregnant, the father of my son started getting abusive. This only happened once (because I left him as soon as it did) he slapped me. And tried choking me. 
My son is now 4 months old. He sees his dad. His dad is really good around him. I can tell he loves him. 
He wants to be a "family" he wants another chance with me. He's joining the military to make my sons life better. (And mine) he says. 
What do you think?