Hi Moon,
I guess I’m confused by the timing as well.
This is my understanding:
Her husband died and she was getting all this attention from his best friend. She wanted more out of the casual relationship, which is totally understandable given they had known each other for a long time. You came on the scene or she was just dating you. The guy didn’t take your presence seriously until you proposed. She keeps living an occasional double life.
For some reason you propose and marry her. I don’t know why you did that but you did. I suggest you hit “RESET” in your brain and forgive her for her past before the wedding, for your own sanity.
It looks like she did delete him from her contacts which is actually good news. He contacted her to send out feelers on how your marriage is doing.
Monitor that phone, dude.
Best,
Inky