What do you think about on again-off again relationships?

my friend and her boyfriend's realtionship is so dysfunctional. they've broken up twice and they've only been dating fo like 3 months. they have little to nothing in common, and they fight a lot. Yet she calls him her "soulmate". i don't understand how he's her "soulmate" when they dont even want the same things out of life. In the honeymoon stage everything is supposed to be all lovey dovey not constant bickering and argueing. when is she going to realize he's NOT the one for her.. if he was they wouldnt keep breaking up and getting back together. and with the excessive affection they display in public im guessing shes just in it for the physical benefits.. this is why i say you cant base a relationship off physical atttaction cause it won't last. she's acting like she's ugly and can't find any other guys.