Boyfriend's impotence?

My boyfriend and I are very in love and attracted to each other but when we try "doing it"...he can't last long. At all. Tonight it took about 1 or 2 minutes for him to get back down. He feels ashamed afterward and apologizes and everything, and I tell him it's okay. He blames it on the drugs that he's used in his past (yes, I repeat, in his past), and I don't know if that's a valid reason or not. And oh, he also smokes cigarettes (as do I), which have been known to cause impotence. We're both 18 and I don't think this problem should be happening at this age. Neither of us are virgins. Is there any hope or is this bound to continue? We do engage in a reasonable amount of ...but I will admit that I have not yet orally helped him out. I don't know if that's even a good idea at this point because it might just make him feel worse if his still goes down. I mean, I don't know. Is there anything I can do about this? Any tips or advice? Thanks in advance.