Don't apologize for rambling. Listening,learning and helping ourselves and others is what's done here.
Like you I came to this site while searching for information and found a lifeline. Grab on. You are welcome.
You said, "I don't know if I should stand by him and help him through it or if I should run so my baby isn't raised always feeling like he/she can't compete with the alcohol/drugs."
You can't stand by him. He's an alcoholic and a cocaine user.
He's a liar. You can't count on him. Your kids can't count on him. You did the right thing tossing him out.
I can't imagine what it's like to be pregnant and have three kids in your situation. I'd be scared too. But if you let this man stay in your life the long term effects on your kids will be devastating.
Kids aren't stupid. You can only hide his behavior for so long.
If he stays around they will grow up in a home where drinking and using drugs is tolerated. Kids don't much listen to what parents say. They "listen" to what their parents/role models do. Actions speak louder than words.
Keep this man away from your children. He's not doing you any good either. You are talking to someone with a brain compromised by alcohol and drugs. His words aren't real.