I would like to point out that homosexuality is a point that the settings team haven't made any stance of the Octarchy public on. As it's a medieval setting, it could easily be illegal or outlawed. Of course, that would enrage a fair amount of people, but making it legal could detract from the immersion of it being a medieval setting.
I'm of the opinion that homosexual roleplay shouldn't include marriage, as if it was legal/socially acceptable in PS, then there'd be mechanics for it. Also note that PlaneShift is endlessly trying to retain a PG13 rating, imagine how bad things would become if "this game is not appropriate for kids. You can even marry someone of the same sex, and as such is only suitable for 18 years and over" came from the ESRB and other censorship authorities.