Hi John -- Sorry you are hurting so much. This really isn't about her feelings for someone else; it's about yours. We can never crawl inside anyone's head and heart.

A line I love from jMiller's Crossing:
Nobody ever knows anybody else -- not that well."

Whether she loves him dearly or has settled for less than you think she deserves -- I don't think that knowledge can make a whit of difference in your own pain.

And the only way out is through it.