It all boils down to choice... Choice, and causality.
You have a choice, you make a decision. The decision is a cause, which leads to a certain effect. Now having taken that decision, it is no right of yours to crib about the effects of those decision.
And when you have a shot at redemption, you want to take it. But the cost of redemption is a blow to your ego. The cost of redemption is the admission that your choice was wrong, you are the cause of the effect that is hurting you. But then, the ego is big. No, it is huge, it is monster sized. So it does not let you accept that you were wrong, that you could have been wrong, that you were the one at fault. So you lose the chance to redeem the things that you pine for, or at least you say you pine for.
It is all relative. The feeling of enjoyment you had when you made the choice was relative, and so is the feeling of sadness you experience now. The fullness then was relative, and so is the emptiness now. The ego you have to assuage is relative, and so are the relationships or lack thereof.
After all, Einstein was not too far from the truth at the time when asked to explain relativity in a layman's words he said, " In the company of a beautiful woman an hour seems like eternity while when next to a furnace and nothing else, an hour seems like eternity."