What happens if you simply stop loving

I realize its been a long time since i have posted anything. And that whatever small number of people used to come to my blog must have stopped coming a long time ago. However, I have a question that I hope you can help find an answer to.

The question that I have is, "What happens if you simply stop loving somebody the way you used to? What do you do?"

Remember I am not only talking about a boy-girl relationship. (And I am definitely not talking about MY own relationship). I am also talking about the other relations. Say you have a long time friend who comes to your house regularly. Or a office colleague who you have to share your projects with. What do you do if you start hating their guts for no apparent reasons. Has it ever happened to you? HAve you ever started "not liking" a person that you used to be fond of and you cannot find the reasons for this change?