Should i feel guilty? Should i dump my bf?!!?

My friend HIlary and I were in the gym the other day and i bumped into this really cute guy (who is now my bf) and today he took me out to lunch. the problem was that i completely forgot that i already asked hilary to eat with me...but she thought i ditched her! i tried apologizing so many times, and i even cried but she was still mad..i dont blame her and i feel horrible! but at the same time she was the one who told me to go out with my bf, plus my bf already told her we might eat together...idk what to do! i feel awul...should i stay with the guy, because friends come first? p.s. i have been so nice to her all year. i bought her things, gave her rides home, and was really nice. i never meant to hurt her, it was a complete accident! what do i do? i already tried to apologize...i am sooo upset and confused and i feel horrible!!!