I wonder if he is with her, what they do together, how I measure up to her
I know it's really hard to stop those thoughts but you have to remember, it's not about you (OW). It's a choice he made on his own. Don't blame yourself for him carrying on w/ someone else. I know, easier said than done.
Can so relate to the attending weddings & family functions alone as I had similarities in my sitch as well.