I think Partner is more socially accepted for unmarried adults living together. Lover emphasizes the sex aspect, and I can assure you that after 15 years together around age 80 sex is a seriously reduced aspect of an important relationship. Far more important is dealing with serious business and property matters, family and grandchildren, and caring for each other when sick. LOVERS???
There really is a lack of appropriate terms for the situation you are in.
Companion seems a bit to casual.
I can see your point about *boyfriend* even though in a way that is the most accurate description of the relationship, even if it isn’t of him as a man.