Forgetting Sarah Marshall VS Serious Moonlight

Just finish watching both this movie and both movies acted by Kristen Bell my favorite actress after watching "You Again". Ok both  the plot are almost the same, about break up and finding someone new in their life but don't you think that is so unfair for someone that already find his or her lover and have been together for some times and then break up just as what they felt they want too??

Forgetting Sarah Marshall was about a guy who date a popular actress called Sarah Marshall and after 5 years they broke up due to the actress date a new male artist and at the end the guy found someone new during his trip to hawaii which was actually he stalking her GF till to Hawaii. I like this story for this movie and thats nice for the guy who found new partner in his life.

Serious Moonlight was about a man who wanna divorce with his wife for another woman. hiswife then prevents him from doing so by binding him to a chair with duct tape. She tries to persuade and convince him that he still loves her, but everything she says fails to change his mind. 

Back to reality, why there are some people that saying such words as loving you forever and never ever leave you but end up they do it themselves???  date another person then at the same time was having relationship with you but end up just fool you and leave you while they dun need  you anymore! that was cruel and they will received the punishment i believe!