I don't think Bob's case is severe, I think it's typical. This holds true for some women also, but women tend to figure it out a little sooner than men. It's the old "the grass may be greener on the other side" notion, or maybe I'll find someone better. Better than what? Are they loving, caring , supportive, and nice to be around most of the time? Hmmm.

They may find someone different, but often not better. It seems to be a human trait of always being afraid that you didn't get the best; the best price, the best looking, the best of everything. If you spend your whole life looking for the best, you will never find the best for you. They are usually standing not too far away.