Am I falling out of love?

My girlfriend and I have been dating for 6 months now. We were both surprised we'd even be in a relationship since we became good friends beforehand. We were happy for the first 3 months or so, still learning things about each other and it felt like heaven. On the night of the first time she told me she loved me, she told me about her crush on her lesbian best friend, she's had that crush for years. However she told me that now I've made her so happy that she doesn't think of her friend that way. As of a month ago, I secretly ran across a few things that pretty much told me she still had a crush on her best friend. She has been going to this friends house and staying there for days, claiming they used to spend the night like that all the time. I know for sure my girlfriend isn't cheating, but she is never close to me anymore, nor does she act loving. We never cuddle and she claims to be smothered by me. I've backed off a little, but nothing is changing. Everytime we talk about our relationship, she says I'm just feeding my usual negativity. She says she is happy when she knows that she can make me happy, however, she never does. I'm not entirely sure what to do, because I'm not happy around her anymore, I just feel like her close friend and that's it.