Ahh, "What if...". Let the what if's go. How? You have to push it out of your mind with something else. I like to go to extremes when they crop up. "What if the sun is going to explode!" I've also used behavior modification with a large thick rubber band that I kept on my wrist and I would snap that bad boy hard when I would start to entertain thoughts that were keeping me stuck. I still do it on occassion.
I saw your post about "how" to detatch. I have to say that I think it's harder with them at home or seeing them alot. You don't get a breather really. Every thought is focused on them the M etc. My H was home 15 months post bomb, and I will tell you that from where I am now, I wasn't detached, not really. It's a process and the more you fill your life and mind with other things, the easier it is.
I still see my H alot (kids) and there are times I still fall flat on my face. The difference is, now I do it with my mouth SHUT. I don't ask a question if I don't want the answer. I am friendly, and I focus on the goals I have. I write them down with steps to take for accountability.
If you saw Mach's post about emotional divorce vs legal divorce, re-read it.