I am sorry to see any relationship break up as it tends to be destructive to everybody involved. One thing I have learned from the site is that when this happens, it's not always cheating. Some people are uncomfortable in an exclusive relationship and need more than one partner. That was a bit difficult for me to understand at first because if I were in a relationship, I would only have one partner and I would expect the same of my partner.
If you chose to, you might still have a relationship with her parents and her children. Separation doesn't mean you have to break the relationship with the rest of her family. I often hear divorce stories where this is the case so wait and see what the future holds.