me and my gf have ben going out for about a year and a month now and it feels wierd. I love her more than any thing. I am extreamly attracted to her. shes my best friend and i am her's but the more shes my best friend the less of a girl friend she feels like i feel too comfortable with her. my history with girls befre she changed my ways was basicly find any chick and make out (thats how we met lol) but because shes my best friend she almost doesn't even feel like a girl to me.
Thats what happened to my ex and me, we were together for 4 years and after awhile he was just a friend and I called it off.
I dated my ex for over 4 and a half years. We were and still are best friends. She's actually gay and always thought of me as a friend. But I found that the better a friend I was the more in love with her I was and more natural my romantic feelings got. Most people aren't like me though. Everyone's different.
Maybe you are becoming what she calls"too comfortable" with her, what's really happening is you are treating her more like a buddy than your gf. Spoil her with love she wants it. Kiss her, hug her, tell her something nice when you all wake up everyday, surprise her with cute notes in her car, or a nice phone call. Things sometimes become stagnant/old/routine spice it up a bit.