ahh sorry to here that to start off. My father was like this with my Mother in Cali, my mom didn't want me growing up around that lifestyle so we left to Phoenix, its possible that your ex can, and then there's the other part of probably not you know? but EddyMetal is right, if you feel like he's worth another chance, then best for you to go for it
Sorry to hear about that. But you can sit him down and tell him that you will give him one more chance but if he goes back to his old ways than its done.
Why not see if he changes (for a sustained period of time) and THEN see how you feel? Especially with drugs, you'll have a better idea once he's sober for a period of years. Otherwise, the relapse rate is high.