taylor: This question needs to be answered by a Lawyer, preferably a Family Lawyer. Tell the Lawyer he has a drug and alcohol problem. I can't imagine they would let him have custody.
First of all, you can't just move and take the kids unless you have a legal agreement to do so. Imagine if your ex got a gf and moved with your kids to another state.
If you do that, he can file to have the children returned and you'd have a mess on your hands.
You need to get a court order allowing your move with the children first.
Second, everything you say about him is considered hearsay without evidence. For instance, do you have police reports documenting the abuse....do you have a restraining order?
Also, what evidence do you have about the drug use. And I don't mean stories...I mean evidence. Has he been fired from a job due to drug use, do you have evidence of transactions for drugs? Courts don't care about what you say, they care about what you can prove with evidence.
Ultimately, both of these allegations may or not affect custody depending on how he deals with them. For instance, if he has used drugs but is getting help now, that may make a difference to his case. The court isn't just going to believe you telling a bunch of stories while you abscond with the children with your new bf. You have to prove your case and get permission to move. You'll also be dealing with him making allegations about you if you go this route.
I can tell you this. Children are a lot better off after divorce if they have both parents in their life. Your bf is NOT the children's father. Unless he's a complete deadbeat and bad father, taking the children away isn't necessarily the right move. Think about what they need, not just about what you and your bf need.
You need to get a court order and unless you're self-repping that means you need a lawyer. Before you do anything, you need to go have a consultation.
You can never assume anything about custody. There's no telling who will get custody. Generally courts will try to keep the children having relationships with both parents until there is compelling evidence not to. They are focused on the needs of the child...not the parents.