In case you check back on here. Some of this might have been said....
I'm going to guess that there is an underlying reason why she is cheating as in a normal, healthy relationship, it doesn't happen.
Once you find out exactly what it is....it might be a little easier to correct. Maybe, she just has too much idle time on her hands.
So, I guess the real questions are: Do you still love her and her, you? Are you willing to forgive her? Is she willing to stop? Are you both ready to make it work? Are you prepared on what to do if she doesn't stop?
In the meanwhile, more cheating isn't the answer and it won't make you any happier. Since, you are best of friends, which is a very good thing, maybe you can work it out...lots of talking is key here to get things back closer to normal. You need to try to understand her point of view, too. Maybe a marriage councelor or close trusted friend can help, too.