Mr. Billup's orientation has always alluded and intrigued me.
I think most evidence points to him being asexual (like his comment in 2x07 "Will it hurt" maybe implying he doesn't experience attraction and his general lack of demonstration of any romantic interest where every other senior officer does).
However, there are a couple of things that might point to him being gay, bi, or pan. His hologram duplicate in Crisis Point: Rise of Vindicta seemed to show almost a romantic interest in Rutherford's character, although it could just be wanting a platonic bestie to share his engineering hyperfixation with (the platonic aspect being seen in his loneliness in the mess hall at the end of the episode). In addition, in 2x07, the soldiers sent by the queen could be evidence of her knowing Billup's orientation.
Almost day is Star Trek Day for me...ππ