Drinking problem

For the last couple of months my boyfriend of almost 4 years has been drinking way to much! He works at a welding shop that his friends dad owns so all the guys there are pretty young and most of them don't have families either. Almost every day after work he'll text me saying he's going with them to buy beer and cruise, or going to one of their houses. My boyfriend is only 19 and it's obviously illegal for him to be drinking. I don't know what to do anymore, he's drinking way to much and I don't wanna leave for something that we can fix I just don't know how to go about telling him I want it to stop, or at least to make him control it more. We don't have kids but have been ttc for 2 years already and I don't want to get pregnant while we're having this problem :(