The more you talk to him and are there for him, the less likely it is that he will ever recover.
Talking to him still is something you're doing for yourself, not for him. You don't really love him. You're just addicted to the salve of him needing you. If you really loved him, you would leave him alone. I don't mean that cruelly. It's just the reality of the situation. Addicts seek each other out because they want to use each other to perpetuate the addiction. He is addicted to drugs, you are addicted to him needing you. Neither of you care that you're hurting the other because the addiction, getting the high that comes from the drug, is the important thing.
You are part of each other's addiction cycle. You being there for him, on the end of a phone or in the flesh, helps him pretend that his behaviour isn't all that bad. Him needing you makes you feel that you're loved and worthy and needed and precious. So you keep in touch even though you KNOW it's the wrong decision.
If you really love someone, you do what's right for them. In this situation, being available to him is hurting him.
You need to come out of the denial that you're in, and see yourself as the addict that you are. You're not helping this guy. You're indulging yourself at his expense.
You need to go to Al-Anon, every day if you can, for a very long time. And you need to stop seeking out relationships with men, probably until your children are grown at least.
I sympathise with you, that you have this problem (I come from an alcoholic family myself), and it's not fair and it's very hard, but if you keep making the same mistake with men then you just need to avoid them for a very long time. If there weren't children involved it would be different, you could muddle through with successive men until you found a good un, but in the situation you're in, you can't do that to the children.
Being an adult means looking at your feelings (about a person, about yourself, about whatever) and realising that reacting to them in an instinctive way isn't always the right thing to do. Because of your upbringing you mistake fear, guilt and obligation for love. But the former three have nothing to do with the latter.