For me it was simple. I want her to know me. If I hide half of my personality, she knows a facade.
Edit: I've been outed by a previous girlfriend and lost all my friends. In my current relationship, married, I was willing to sacrifice all my friends again, and willing to completely be out, move to Frisco, etc. if she rejected me. It was my do or die time for a hetero-quasi-normal relationship. I wasn't gonna try anymore. After her, it would have been gg admirers, other CDers, or maybe a man. Point being, I was sick of the hiding, guilt, and ostracism. I drew a line in the sand and said I ain't taking it anymore, either she accepts, or I'll seek my own kind.