What he does without you isn't for you to worry about. He's an adult. He managed to get along before you were around, he'll manage when you're gone. He'll have to figure out the child support, custody, work etc. That's what adults do.
The best thing you can do is take care of you. Get out of his path, leave him to find his way. Having you there to take care of things may be keeping him from facing the very consequence that could turn him around.
You have one life, and you deserve to make that life the best possible. This isn't it. Relationships sometimes don't work out, for whatever reason, and it's okay to realize that and move on.