Ausdauer and Durchhalten as far as I know mean persistence and endurance - but they sound more impressive in German for some reason. We sometimes lose what we might have gained by giving up too soon.
I wonder if this is what happens to some of those film stars who get married half a dozen times (and no doubt this happens to other people who are not famous so we don't know about them). In that first falling in love, or perhaps in the slower development of a relationship that grows on us more gradually, we see everything beautiful and wonderful about the other person. With more time certain things we used to overlook start to irritate. Perhaps when they irritate or even exasperate enough we start thinking that we should move on, look elsewhere. This is the point at which to apply Ausdauer und Durchhalten.
It does sometimes happen that a situation is beyond redemption and it is better for all concerned to move on. But first one must consider what in the situation might be redeemable, and what efforts one must make oneself. Thinking about what changes the other person must make will not achieve anything useful. And endurance and persistence can sometimes lead to surprising results. Just as a couple who have been through a difficult external situation together become closer to each other, so it can happen if they successfully negotiate difficulties in a relationship.
In other areas of life, too, success usually depends more on persistence than anything else. Why am I not a very rich successful business person? Because I am not fixated on those goals enough, I do not put the necessary effort into those things. Not because there is anything fundamental in my nature preventing it other than the lack of sufficient desire.
Not to worry: decide what you really want (that's the hard part) then go for it. And like a child learning to play a musical instrument, don't get put off because you cannot play Beethoven after your first lesson.