Not very well, unfortunately. People that were important to you seem to leave bits of your past together lying around like psychic landmines for you to find. The good news is like landmines they seem to be one-time use, so the more you plod about in day-to-day life and run into them, the more will be safe. The bad news is at least with me, I have to experience the memory-reconciliation crap about an event before it is safe.
I went through a really bad break-up about a year back, and for the first couple months everything from my toothbrush to the weather would remind me of the good times with the dude. After that, they got more far apart and less intense in that "I need to call right now" kind of way. I'm in a new relationship now, and only really bad on some holidays and such.
When these things do hit, they hit hard even for a mostly healed person, and I do not envy you the experience. Now that I have a new mate, I talk it over with him when this happens and he has this amazing calm that helps me to see things clearly again. Before I had my new man I used to go spar with my hapkido buddies (reasonable idea), take a bubble bath and then distract myself with ice cream and video games or a romance novel (good idea) or drink (really, really bad idea).