The key to lasting love

 
Q. Want to know what causes the dissolution of far too many relationships in this world? 

A. I can tell you how it goes in three acts:

Act I: You hurt me.

Act II: Because you hurt me, I hurt you.

Act III: You hurt me even more because I just hurt you, so I hurt you even more. Then you hurt me; then I hurt you; then you hurt me because I just hurt you, so I hurt you more, and so on.