HI Rollin,
I second what Carolyn says.
You love this man. However, it's too soon to consider marraige.
Only down the road, and only if he gets treatment, stays on the medication, and I would also advise he should see a therapist once a week. If he doesn't have the money, he can get SSD or SSI from the government which will pay for an outpatient clinic.
Show him your love by offering to go with him to the psychiatrist. Give him support and encouragement.
As Carolyn said, if he doesn't work on his health, you will have to be his caretaker in the marriage. That is not healthy for you.
Please consider what you are about to do. If I were you, I wouldn't push him to marry you right now.
I wish you all the best.
Regards,
Chri