Me and my ex divorced eight years ago. Now that the kids are grown, he suddenly wants cusody. This scares me to death. I'm the one who sacrificed for my children and now that they are 11 and 12 (a bit easier to take care off) he wants them. He has been behind on child support, has a drug use history, but is fairly stable right now and makes a lot more money. This feels so unfair!
I would need a lot more information to access the situation, and I'm not a lawyer, but I do know that the judge is going to look at more than just the situation recently and how big the paychecks are. It takes more than money to raise a child! If your ex has a history of drugs and has been behind on child support, that is definitly going to hurt him in court. Do your homework. Find out what the laws in your area are, and I would definitly retain a lawyer early.
You have the kids now, and if you have been doing a good job raising them, it will be very costly and difficult for him to just step in and take them. I know this is very painful and stressful for you, hang in there!