i believe humans are still selfish in nature.
when we are in a relationship, we may know that someone out there might be having some interest in us, we will not give a damm about him/her. we prayed that the person will get a partner soon so that he/she will leave us alone. i mean nothing is wrong with that as we ought to be faithful to our partners but ignore or detest the person is not something we should do.
however when we are out of the relationship, we suddenly feel that we have lost the most importantl thing in our life, and we start looking for another person to fill up the space. dunno its coincident or we try to look for simple alternatives, we begin to turn to the person we used to ignore. haha! the world is always so interesting: that person has found a partner and has plans to get married. haha double blow. jealousy steps in next. we say and do all kinds of things that will prevent the 'unwanted' outcome.. but is that morally right?
what rights do we have for doing that to break up someones else's relationship? do we really have the person's interests at heart for doing all that? are we sure we can give him/her more 幸福 than the other? are we doing that because we really love the person? or it is a selfish thought in us that wants to keep people by our side as 'spares' rather than giving them the opportunity to find their real happiness?
we should remember that we chose to give them up in the first place, and finding their own happiness is their choice.. and we ought to respect their decisions instead of being selfish.