Happiness is the point of life. It's very clinical, but any relationship should be considered whether it makes you happier or less happy. If you sever a relationship will it make you happier or able to pursue something that might?

My wife and I were having a difficult time a few years ago. I told her I'd fight someone else to the death for our marriage. But I won't fight her if she thinks she can be happier in another situation. I want to work through our issues (which we did) but I'm not going to argue and try to convince her to stay because we would both be sacrificing happiness at that point.

(Special exception to your kids. Hopefully they make you happy, but you do "owe" them parenting to a certain point.)