When you break-up with someone, you don’t want to date them anymore, but you don’t want anyone else to date them either.
Just like as a kid, you have outgrown your teddy-bear and you don’t want to play with it anymore. However, if anyone else expresses interest in playing with your teddy-bear, it is very upsetting.
Friend #1: I can’t believe it – I broke up with him, not the other way around, so why am I so upset that he is dating someone else?
Friend #2: It can’t be helped, it is called ‘Teddy Bear Syndrome’, you don’t want to play with your teddy-bear anymore, but you don’t want anyone else to play with it either!