What if she was wayyyyyyyyy hotter than you? 
Younger? Yes.
Wayyyyyyyyy hotter? Unlikely.
I just love how altruistic everyone thinks they would be in that situation. I'm not saying they have to get along but it takes a while (years!!) before the marital issues/baggage gets fully resolved. Therefore, adding another person into the mix doesn't usually bring out the best in people until those other issues are resolved.
A huge part of it is how/why things ended in the first place.

HM is in a unique position because marriage and a new baby will affect the resources (time, money, attention, loyalty, etc...) already being spread out between his various commitments. Also, his girl's 'helpful friend' will be losing a running partner. Even if people don't consciously think about these things on some level they are aware and end up acting in what they feel is their own best interests.
I just believe this is a situation where women don't like to admit 'issues' may still exist. There can be various reasons for the issues but they still exist on some level.
