Another related life lesson that I learnt the hard way:
When you are deciding whether to get back together with your ex and your friends tell you to write a pros and cons list.... DON'T. Furthermore, NEVER let your friends add their own thoughts to the list. And, finally, IF you are too stupid to follow the above advice, don't be so stupid as to let your once-again girlfriend find the list. She won't see the funny side. Probably because there isn't one