Well, using marijuana is still using drugs, just a different one. And that he claims it is for anxiety and migraine relief is just an excuse, as you say, for not being ready to cope with the ups and downs of normal life.
I'd suggest putting the focus squarely on you and what you need and want. You need and deserve the time and focus for yourself.
He'll pull you back and forth with manipulation, all of it intended, at the core, to rationalize his drug use and keep on using. Is there any way you can live - or visit - somewhere else for a while to take the time to think this through?
Shooting Star1