Though, I haven't gone through such a situation in life (Alhamdulillah) so I might not be able to give a better opinion than those who have actually suffered, but I do relate this situation (in a certain way) with any major loss or disaster one might go through in life.
It is a human nature that whenever we are going through a tough time in life, we tend to find the grass greener in our past, and our mind might forget all the hardships that were associated with those times in our past. We feel that our present difficulties are the worst we ever faced, which might not be the case and hence we lead our mind towards pessimistic thinking.
In order to move on, we need to learn two things:
To forgive ourselves and realize that we were not that bad human beings that we decided to separate from our life partner for no genuine reason at all. S/he definitely gave us strong reasons to force us to take such a step. Though that step might not have been the best step we took, but at least it was not the worst step either under the circumstances that were created, for which s/her is also responsible.
All the other potential life partners whom we think could have been better than the ones we left / divorced would look gorgeous and amazing to us because we haven't spent enough time with them to be able to see flaws in their personalities. If a person was very nice, sincere and kind to us in a **very short meeting **doesn't necessarily mean that he would have been the best choice for us, because we didn't get enough time to know him/her completely.
Life is too short, death might be waiting for us in the near future. Every step that we took in the past, whether good or bad, made us more matured, helped in the development of our personality and is now a part of our experience which we can utilize to make our future better, ONLY if we are ready to learn from it and forget the wound it caused to our soul. A diamond in a crude form is only purified after it goes through fire, so that time has now made us a more loving, caring and sincere person who would never take a relationship for granted in the future.
There are people who have suffered through the worst times than we might have seen, but they were able to move on only by thinking " When the heart weeps for what it has lost, the soul smiles for what it has found "
One's new life partner has a right over him/her in every way. As s/he is living with us now and each and every moment he is spending with us, some of the flaws in his personality might look a lot worse then that of our previous potential life partners only because we have been exposed to his activities more than them. If due to negative thoughts something bad happened to our present relationship with him (Allah forbid) then in the future we might be weeping in the same manner for our present relationship the way we have been weeping for our past partners / potential partners.