Nowadays it is too easy just to walk away from a relationship. You need to work at it. There is always going to be good and hard times. You need to work through the hard times. It is so easy to just find a new partner nowadays as no one seems to stick at it anymore, and no one seems to care.
What you need to remember is, if you want to go off with a new partner, there is no going back. You have broke the trust and once that has gone, the relationship is gone for good.