Why do I feel so confused all of a sudden?

I am a female and I'm straight as of right now, I'm in a three year long relationship with a male and I've been begun to feel a bit strange lately in the past year. I find whenever I view porn I only look at the woman and I find the womans body so beautiful and I don't really get turned on by the body of a man unless I'm in the act of sex in which I do. I do not notice the attractiveness of men very often but it seems like everyday a woman's looks catches my eye and I think how beautiful she is to myself. I never get nervous around guys anymore and it is always women that I get nervous and I can't think what to say and I'm very conscious of how I am appealing to them. I've noticed all these changes take place and it's left me very confused because I've never been with a woman- in any kind of sexual way or even kissing and yet now I wonder to myself what it would be like to have a woman as a life long partner instead of a man. I love my boyfriend very much but these feelings are so strong and I don't know what to think about them or even what to do, I'd really like some advice if anyone has ever been or known any one in a similar position