Hiding a GAY relationship

I have been dating a great guy that I met on myspace for 3 1/2 months now. He really treats me right and has done eveything for me in this short period that a women hasnt. I live with my sister who of course has no clue. I dont give off a vibe of being "gay" at all so thats not a problem but everytime "shes" brought up its hard to talk about "her" when "he" is the real topic.

I know its another hurdle too jump over but should I come out and at the same time let my sister know who im having a relationship with or continue playing the role of "her,"?