If he isn't there for one baby, he won't be there for another.
If he wants to see his son he will see him regardless of the decision you make. He's just spewing empty threats to try and control you. They always use the child as a pawn to get what they want but you do whats right for you and I would also suggest getting a custody agreement so he cant do anything stupid.
Any man who used my child as a pawn in his games would not be welcomed anyhow. I would honestly abort. And, to be frank, my daughters are 13 months apart, and it was fucking hard and trying.
Personal experience says, he wasn't there for the first he won't be there for the second. Sure, people change.
You have to make this decision based solely on what's best for you and your son.
You have to do whats best for you and your little boy.
If the father is shady now, he will be shady later. Don't keep the baby because thats what he wants (if its not what you want too).
Make the best decison for you, not him.
You and your little one of course!