I would have to say that, yes, generally speaking people in a long term, committed, relationship do. However, if your boyfriend is apprehensive — I don’t feel right about pushing him into going without a condom. (Perhaps he, or someone he knows, had a bad experience?)
As far as why they don’t sell large condoms as often as regular size… I think the answer to that is self evident. If there was as great a demand, they’d offer them because they’d want to sell them. (Stores want to make money after all.) Your boyfriend is not the norm and is (some would say) gifted in this area. 😀 Perhaps they don’t want “small” to “average” guys to feel bad about not being as “gifted”? 😉