My heart goes out to you, MM. I've just recently found out that my ex is getting married next month, which shook me a bit. But it didn't make me feel as bad as I thought it would. I expected to feel more hurt, I think, and I was quite happy to see that it didn't bother me that much.
And I think the main reason for that was time.
We broke up quite a few years ago now, and at the time we both wanted to stay friends and be honest with each other. Several weeks after our break up, I found out that he'd started seeing someone else straight away. and he hadn't told me. That kind of destroyed any real friendship between us, because there was no trust.
I know your situation is different, but don't take the healing force of time lightly. For your own sake, try and get some time to yourself, so that you can get your locus of control back inside.

ding"thinking happy thoughts for you"dong