Greetings Airwalk,
You are at a very difficult stage of life. Discovering who you are can be a riddle at times and understanding your sexuality can be downright confusing. Especially if you think you are experiencing bisexual feelings. I know, I've been there.
I'm a 37 year old bisexual male. I'm currently married and have an adorable 8 month old son. I've known that I've been bi since I was about 12 years old. What being bi means to me is about being sexually attracted to someone whom I am very emotionally close to and also find physically attractive. Usually, I am attracted only to women. When I see an attractive woman walking down the street, I look at her (I try not to stare.) I don't look at men that way. However, there have been a couple of times in my life where I became physically attracted to some of my male friends. I've had several very close male friends in my life, although I was only physically attracted to two of them. One of them, as it turns out, was bi and we were lovers for a couple of years. We were not out of the closet, but met discreetly on occassion. We kind of drifted away from each other as lovers when we developed relationships with other people. I currently am in a monogamous relationship with my wife. We love each other very much and she knows I am bi. We are married because we love each other and we wanted to raise children together. My former lover is still one of my best friends (yes, my wife knows about him.) I guess if I have any advice for you is that you should communicate to those you love and are attracted to about your feelings. I don't think it is wrong for you to have the sexual feelings you currently have. You've told your friend that that you find her physically attractive. That's wonderful that you two can talk about it.
I'm going to make a generalization and say that I think it is a bit more difficult for young males to come to terms with their sexuality than young women. The reason I say this because there is this macho, bullshit attitude that is ingrained into boys which conflicts with their sexual feelings for other males. I think a lot of young men turn into violent homophobes because of this internal conflict. Females don't seem to have this problem.
By the way, I think you are very normal, though a bit confused and depressed. Since you are currently confused, I suggest you don't rush into a marriage with your (ex)boyfriend. I think Joelbear also had some great advice.
Peace,
Ray Skyhorse