Getting into medical school is hard under the best of circumstances. I am sure getting through it is even tougher, but don't let other people dictate to you what is possible or not.
I was lucky and my husband has been very supportive (even when he was just a SO). He was great during undergrad when I studied all the time, great when I applied, but I think he was more theoretically supportive. We compromised on the schools I would apply to, but when I actually started interviewing in places like Providence, Boston, Rochester, New York, etc...he started freaking out. I believe his response to my interview invitation from Harvard was, "It's cold there." I was frustrated until I put myself in his place and realized he was just scared. Scared of leaving his job, scared of the cold, and scared of losing me. Perhaps your SO is just afraid he will be you will grow away from him. He may just need time. A few weeks ago my husband actually encouraged me to write a LOI for Mayo, and that is in the coldest location by far. He said he decided I deserved it
Anyway, as I said- don't let other people tell you what is possible. Not every school has you in lecture for 8 hrs a day. I know for a fact OHSU (your state school) has class 4 hrs a day most days of the week. It isn't impossible to have a healthy relationship while in school. When people fail at something they will tell you it is impossible. Just tell him how you feel and hopefully he will turn around