Most Helpful Guy
It really depends on what's more important to you -- the friendship or a potential relationship. Also keep in mind that when you all graduate high school, the relationship is unlikely to survive that transition unless you both end up in the same area after you graduate.
Most Helpful Girl
Firstly, no, you are not at fault for remaining friends with him, and you absolutely shouldn't give her the power to make you feel guilty! If you want to tell him how you feel, do so. But maybe you should have a talk with your friend first to let her know that you value her friendship and that she's important to you, but that she can NOT dictate who you or your friend chooses to date. Your relationship with your guy friend is your business. Tell her you need to get your feelings off your chest and tell your guy friend your feelings. If he should reciprocate, great; decide what you want to do with the relationship. If he doesn't the problem is hopefully resolved! Let's just say he did like you though. Would you really let your other friend more or less push herself between you and your guy friend? You did nothing wrong. She is still hurting because of their breakup and she's looking to take it out on something or somebody. That is not what a true friend would do. If she wants a shoulder to cry on and an ear that will listen, she should ask. But she's made her intentions clear and she could damage things between you and your bestie. Good luck and follow your heart!