You stop. You stay busy doing things you enjoy, you go out with friends, you go for a run, you go to the gym, you do whatever you need to do.
When your mind starts going to all these negative places---where she is, what she's doing, etc---ask yourself, "Is this something I can do anything about?" If it's not---and not one thing she's doing/thinking/feeling/planning is---stop. Take your brain in your hands and turn it somewhere else, manual change of topic. You'll get better with practice, and you'll feel muuuuuuuch better when you're not dwelling on things you can't control. Take control of those things you can control: you.
And give yourself a break! It's only been two weeks, and you're probably still dipping into panic mode. That's natural. Remind yourself that it's not over, you won't be divorced tomorrow, and that it'll get better. It really does, by the way!
You have a lot to think about---your role in the problems, etc---but you can't obsess about it. You're doing really well, so be patient with yourself.
