Hi confused,
It is normal to find other's attractive and admire the positive things we see in them. But whether Bi or not, the end result is the same.....She's off limits

. She has a partner and you have a boyfriend.
You could just be more curious then anything but be sure and respect the fact that both of you are currently in relationships.
She may be hot, but she's taken. That applies to any sort of relationship bi or not.
Don't be so hard on yourself and fret about what you are, just be who you are, which right now, is currently in a relationship. You may want to ask yourself if you are happy in your current relationship, or are there reasons, you mind and eyes are wandering so much.