Oh...she did it again!

Some things seem right, some not so. If I believe that there is no such thing as right or wrong, all that exists is a perspective. What is right for you may be wrong for me and whats wrong for me may be right for you.
Then why do I feel some actions are wrong? Maybe its my perspective? I sound confused, I know.
The question in my mind is very simple, why would a girl who is madly in love with a guy and who has been with him for atleast 3 years suddenly dump him and go for another guy ( one divorce, one failed live-in relationship & a roving eye no less!)
I understand it not! I am not against people's choices. Its their choice after all! A decision as impulsive as this? I may be judging it wrong, but it bothers me.
A girl gets out of difficult relationship and meets a good samaritan. They fall in love and live happily ever after? No- they are happy together until one day the girl(with a smashing career) meets another guy (better?) and drops the good samaritan like hot potatoes and moves on quickly and how! Maybe the right guy came along a little later, so who was the good samaritan a temporary arrangement?
One fine day, can you really realise that the person I loved all along was the wrong choice? Instead the cool guy around is the right one? Well may be. It can happen but hey, not in a week's time! Give it time folks, its love- you need to nurture it , let it grow and try not to uproot it to count the roots. It takes a long time to grow into a tree, to destroy it and plant a seedling for a new tree is all great but is it worth? Well, its up to you to decide. I still cant digest it!
May be, marriage has domesticised me, or has it made me narrow minded? Whatever it is, I dont think it wise to make impulsive decisions in love, then it becomes a game of luck, if you are lucky, you get it right or you are left in the blue!