I struggle a lot with this myself, and my success rate is not great. When I am obsessing over What Ifs, sometimes one of these strategies helps:
- Distract myself with light reading or TV.
- Clean something, preferably while listening to a podcast
- Imagine the worst that can happen and realize that I will survive it
- Remind myself that all of my wonderings are just stories my mind makes up, and I don't know what is going to happen, so it's not helpful to listen to the stories

Hang in there!

Me: 44
H: 44
Kids: 20, 16, 16, and 10
Together/Married: 22 years
H announced he was emotionally detached and considering D: 4/4/16
H announced he is going to try to stay and reconnect: 5/1/16