My boyfriend is a pothead, any advice?

I've been in an on and off relationship with this guy for a little over a year and i love him very much. We've had a lot of problems with our relationship in the past, which we've seemed to work out, but his weed addiction has become another issue. When i met him, we would smoke together every now and then, which i don't believe there's anything wrong with. But gradually he started smoking more and more, and now he's getting high with his friends several times a day, every day. Whenever i see him, he's always high. He's not the same person anymore. It's like he's not even here and i feel like our relationship has become very one-sided. He is 26 years old and i don't know if he'll ever get on with his life. I'm having a dificult time deciding whether i should wait for him to change or just let him go..