Ooh! I like this topic! When I started dating Jocelyn, I had a little problem with wanting to "be the girl". I had starting focusing really hard on treating Jocelyn like a girl (because nobody else had ever done so) Of course, she was thrilled and it made me feel good to make her so happy. After a couple of weeks of my holding her like a girl, dancing with her like a girl (my hands on her waist, etc.) planning all the dates, always having to call her first, etc. I started feeling like "the guy" and as androgynenous of a personality I can have sometimes, I didn't like it one bit.
On Halloween I dressed to the nines in a short skirt, curled my hair, did my make-up and when Jocelyn came to the house I announced (rather sarcastically) that I was "going as a GIRL for Halloween, imagine that!" Well, we had a nice long, tearful discussion and when Jocelyn explained to me that she wanted us to both "be the girl" I calmed down a lot.
Now we trade off doing things. Sometimes she'll open a jar for me that I can't, hold me with my head on her shoulder, carry bags for me. And then it's my turn. It sounds complicated but we really don't keep track of who's doing what anymore and it's become rather comfortable. The only "girl" thing that we don't trade off is cooking because, well, she's needs some training in that!
I don't feel like I compete with her at all, but that may be because we have almost the same height and build. I also don't feel like another woman is taking my space. We'll be sharing a bedroom soon and I'm really excited that I'm going to get to have a purple bedroom without having to compromise for a more gender-neutral color. I also really like being able to share clothes and make-up.
I suppose that she doesn't threaten my femininity because I've already gone through something else that did. I felt like only half a woman when I was told that I had a hormone condition that may prevent me from having children. What I had to realize was that no amount of hormones or physical complication was going to make me any less a woman than I felt that I was on the inside. I feel that it was an important lesson I learned. Without knowing that, I don't know how I would've handled the problem that I had in the beginning.