AITA for wanting to put an ultimatum on marrying my partner.

I (23f) just recently got engaged to the man (27m) I love oh so very very much.. he -actually we- have very very addictive personalities and he’s always used substances to run from every uncomfortable feeling he’s ever experienced. When we first started talking/dating he would smoke weed every 5 minutes (LITERALLY) and I told him then I think we should go separate ways because we live different lifestyles as I’m only interested in partaking recreationally on the weekends or something. He insisted on change because he wanted to keep me in his life and now (that I know of) he has cut to once a day in the evening. No more before, during, or directly after work.. no more driving high or anything to that effect. Well he keeps talking about doing even better about it and we even put a deal in place for this week Sunday through Wednesday neither of us would smoke (because he wanted to prove he didn’t have a problem) but he broke that deal immediately Sunday and again Monday.. here we are Tuesday and I’m certain he’s gonna do it after work because he’s got into it with a coworker. I can’t live my life that way and I hate being with him while he’s high and I’m sober (because he becomes a dumb child that will not remember anything or makes zero sense even talking). Many people are saying I need to tell him that I’m not marrying/ moving in with him until he gets his addiction under control completely but I am scared to do that because I’m scared I will lose my best friend. AITA if I put that ultimatum in place?