The lost time is something which hurts a LBS more than a WAS. It seems the WAS is having the time of their life at our expense. The biggest gut-wrencher for me is this feeling of "Hey wait a minute. We worked ourselves to the bone building a family, building a career and planning for a golden future. Having got through 10+ years of marriage, having turned 40ish, and getting ready to enjoy the fruits of our labour, you selfish idiot destroy everything! I don't have the time, energy or motivation of a 20-something to start again."
The only way to deal with this feeling of loss is to ensure the days ahead of us aren't loss (we GAL till it hurts), and to realise that our spouses didn't maliciously plan to hurt us in our vulnerable middle-age.
Whatever one says, whatever one believes, and however one gets through this mess, its still a journey through the darkest corners of hell.