Parents talking to your daughter about being bi...?

My daughter is seventeen and she just graduated from high school. Her sopre year i was looking at her text messages (randomly while she was in subway) and i discovered that she had started to like other girls. I approached her about it but she was defensive at first, but she finally came out about it and told me she was bi. Now at seventeen she has had a year long relationship with a girl and they are inseparable. I guess my question is, what do i do here? I was raised that the right way is a man and a woman, not two of the same . I don't know what to think or how to approach her and her girlfriend like a regular couple. Any parents offering some advice would be helpful.