Why?

Ever wonder how a man can tell you that he's meant to be with you and that he doesn't want anyone else, but can break up with you the next day and find someone new the day after that? Why can't it be true that a person really loves someone and they really don't want anyone else. When it's like that, they try to think about someone else, but it just can't happen. They are obsessed. This is not healthy, yet everyone is looking for it.
Let's look at it like this, you love someone, but you don't believe that they are the only ones you'll ever love and you can love as many people as you want.

Serial monogomy. It's replacing marriage and commitment - I mean, you do commit, for now. So Mr or Mrs Right Now never becomes Mr or Mrs Forever.