Make sure the stay away from alchohol and take their Lithium tabs daily!
If you are in a "long term relationship" with said person, are they not already in a "real relationship"?
you tell them to make it real or you're gone. then follow through.
well arent yuo saying this person refuses to be in a relationship with you? then theres nithing you can do but dream about them for decades and love them from afar. they have to be willing and want that relationship.