I think it is to do with loyalty. If you start to date your friends ex then you are not being very loyal to your friend. Its just one of those things i guess !
It befuddles me when people come out of a relationship and they want to get into another one almost immediately. Or when people always seem to want to
be in a relationship, they are always looking to be in one. They have never really spent that much time alone because they have always had a partner.
Just sounds too complicated for me !