the only reason women are able to walk away so cold heartedly is two fold...
1) they see themselves as a victim and actually blame you for whatever has destroyed the relationship (they aren't honest enough with themselves to say 'sorry, frank is a doctor and ill have a better life with him so im dumping you')
2) they spend months mentally archiving every single little thing you do that could in any way be considered rude, insensitive, mean, etc. they build this list up so that they can at some point say to themselves 'this is crazy, why am i with someone that treats me like this.' (they do this to support the first point i made above).
women are cruel when they leave because they have spent months creating a delusional image of you in their mind, making you out to be an insensitive jerk who has actually taken advantage of them and has wasted THEIR time (months, years, whatever).
its pure delusion, but they believe it. the REALITY is they dump their man because someone that they think is better has shown interest in them. but to admit to themselves that they approach the world with this 'gold digging' mentality is unlady-like, so they will actually convince themselves and honestly believe that they are leaving because of you.
as for a man's capacity to cope with a woman leaving and how they do so... all i can tell you is that there are much worse things in life than a woman leaving. a family member or friend dying is much more painful than having p*ssy walk out the door.
but the worse mistake a man can make is to place his happiness in the hands of a woman. to NEED her. or even to NEED to be her protector. guys often underestimate how powerful it is when someone needs you. it gives your life a 'purpose' that often is otherwise missing.
women experience the same thing when it comes to their kids. take a child away from a mother and she falls apart. in some senses, i think taking a child from its mother is similar to taking a woman from a man - both exhibit the effects on the protector and the impacts of having that which is protected removed.
this is why women are able to move on from a man more easily than the man - because she was not protecting him. its actually harder for the protector to let that which he was protecting simply walk away. its as though that which defined his greatest worth (ie. being a protector) is now gone - and he is left wondering what value he has.
to understand the female mentality, think of working for an employer. you may give years of yoru life to that employer, but when a better job comes along you move on. its not necessarily easy, but its not devestating. because you feel no obligation to protect the company - you just accept its time to move on.
women see men in this way. but men don't see women this way. men become accustom to the role of protector - feel as though finally they have value, that they are the KING protecting his queen. but when the queen leaves he goes back to being a peasant and it hurts.
im a strong proponent of the zen philosophy. you cannot control the world around you. you are not any one thing. you may act as a protector, but it is not WHO you are. you may act as a bf, husband, father, but you are not solely any of these things.
at all times, you are merely a human being, making his way through this experience called life.
make the best of it. do not worry of the worst, becuase even if it comes you will survive it. do not wish for the best, for it will come in its own time. simply do your best to be the best person you can be at all times.
if you do this then even if you must walk this earth alone, you will do so in contentment.
and know as well, that male or female, anyone who does not live by this philosophy will suffer. so while a woman man branch swing, check back with her in five years and you will see she is just as miserable, if not more so, than the day she left you.