Erection problems

My bf is 30 and I’m 22. We have a really nice relationship and love each other. We began having sex and he has problems maintaining his erection. He smokes, so I think it could be related to that. It’s hard to have sex, because he only gets a strong erection if I give him a blowjob or if he’s really really really turned on, but this doesn’t last not even for a minute. He gets like 60-70 % hard and I manage to do it with that.

Do you girls have any experience or tips with this? I don’t wanna tell him anything directly because I know it’s a difficult topic and I don’t want him to feel bad :(