Welcome to the board.
My first thought was not drugs, it was "holy moly, I am 18 and about to become a dad". I bet he is scared to death. People lash out when they are afraid, and fear comes off as anger often times.
This will be a cold splash of water in your face, but the best thing you can do is stop helping him. Stop paying his rent. Stop helping with money in any way. You did not get his girlfriend pregnant, he did. He has to be the one responsible, not you.
As far as getting him help for his anger, take it from a veteran. You cannot make ANYONE get help until and unless they want it. If he winds up in jail, that will be his lesson.
If the time comes that you are truly worried about the unborn baby, and there is no other place for the girlfriend to go, then you might consider moving HER into your place.
Tough love is not an easy thing. But as our difficult children get older, it is very important.
Again welcome to the board. Warm hugs and prayers your way.
