Alizgi, so sorry that you are living this.
But you sound as if you have your head firmly on your shoulders. You are right, you need and want the best for you, your son and your baby.
Time will tell if he really is capable of cleaning up his act.
Just please don't get into the cycle of giving one more chance after another. Today you sound strong enough to make the right choices and décisions and see them through.. if you do get sucked in to a negative downward spiral in dealing with his behaviour your clarity and resolve will start to wane with time.
Stay close to the folks on this site. They will be a great help.
Wishing you all the best.