IMO, eventually you're going to have to choose between a 20 year friendship (is this your BEST friend?) and a relationship with this guy. If she is still hurting over the breakup, she will never forgive you. Even if it was her fault.
So, you will have to decide which will hurt you more: losing her friendship or losing this guy. I think it would be different if she were safely married (when is her wedding?) Also, what does HE have to say about what happened? Is he still hurting over her? A lot depends too, on how much of an attraction there is between you and this guy. If its undeniable, I say go for it! but then, Im the one that cant count how many people Ive kissed
