Hi Bethann....
You're moving in the right direction. Posting here instead of blowing up at your boyfriend is wise and healthy. Have you considered joing an al-anon group?
I take it he's aware that you disapprove of his pot smoking? All you can do is say how you feel, it's up to him whether he respects that or not. Then it's up to you to decide what you're willing to put up with. I urge you to refrain from giving him ultimatums unless you're prepared to stick by them.
Your boyfriend needs to figure out what void in his life the chemicals are filling. Maybe you can help him do that, or maybe he needs to find counseling or a group. Try not to approach these subjects when you are angry or tearful. It's likely to provoke resistance.
Welcome to the forum! Keep posting. We care.
Smoke