I agree that boyfriend/girlfriend often starts to feel weird after awhile. For me, I started feeling strange calling my now-DF my boyfriend...actually, I was never really comfortable with the term. Part of it is because we dated long distance in the early part of our relationship, so I didn't really talk about him then. By the time I started actually talking about him, because we finally lived in the same place, it just didn't feel right to call him my boyfriend. I think his age had a lot to do with it, though, since he's 5 years older than I am.
I tended to use "boyfriend" anyway, though, unless I could just call him by name. Everything else was even more awkward for all the reasons already mentioned.
I was actually kind of relieved when we actually got engaged, because for whatever reason, "fiance" sounds a lot more appropriate than "boyfriend." I'll be happier still when I can just call him my husband and be done with it.