What she feels for OM is NOT love... She's in an altered mental state and isn't thinking clearly; trust me... Karma's a b!tch, and she's so messed up right now.
One day, after you've moved on, she'll be begging you to take her back. But, sadly... It will be too late because you'll be OVER it!
How do I know? My college sweetheart cheated on, even after we were engaged. It killed me at first, but eventually I realized HE had the problem, rather than previously thinking I wasn't pretty enough, etc. Well, he was pretty stunned when I refused to marry him -- still calls me to this day 30 years later... After a while you just get sick of the abuse, and you don't get hurt anymore.... You get ANGRY, then... Even better...
You just don't care! I know it 's more complicated with kids, etc. But you will get there.
Get out there and play the Glee version of the Cee Lo Green song "Forget You!"... I'll try to post a link to that from YouTube because music has been great therapy for me these past few weeks. Distraction helps with addictions!