drug issues and my bf helpful advice welcome just don't be a dick

so I've been officially with my bf for about 6 months now, but I've known him since middle school. I'm 19 and he is 21. he has been a frequent pot smoker since he was 12, and I started as well around the end of last August. I have since discovered that I should not have ever gotten anywhere near the stuff. it does some really weird things to me, and is extremely detrimental to my mental health (I've seriously struggled with major depressive disorder and severe anxiety since i was 10, I have a lot of mental health problems generally speaking). So, I have been trying extremely hard to just stay away from that shit, but he wants to go and get high all the time. And I've told him that I really need drug free relationships and a completely drug free life, and if he would rather be high all the time then our relationship will not last. i told him that if he hasnt quit by early june we are done. And that is really really hard for me. I love him so much and he has always been so good to me, it breaks my heart to even think about it. but this is something that's important to me. I just don't know if I'm being stupid, or overreacting to everything. I feel sick and I don't know what I'll do if he doesn't quit, this whole situation is very scary for me.