You may feel different from your girlfriends, like you don't fit in sometimes. When your girlfriends are checking out the guys, you may find yourself checking out other women. Going out with men may not interest you. You may also feel confused or unsure about whether or not you're a lesbian. You may feel confused because you're attracted to both men and women, and that's okay.
Some women have relationships with both men and women throughout their lives.
Some women eventually decide to be exclusively lesbian or exclusively heterosexual. Sexuality usually develops over time, so don't worry if you aren't sure. They don't understand that there is love involved, too. Whoever you fall in love with, that is normal sexuality. Normal is in the eye of the beholder.