How much is enough?

Most of us at some point in our lives, had relationships that seemed to dwell in a particular setting: no matter how much you try; how much time you give; it still seemed to have the same issues. And the difficult part is that because you love the person, it makes it all the more difficult to move on and look for another relationship. Which brings me to ask the next question - how much is enough? How much of the trying, waiting you have to do? Or should you just accept that the relationship is what it is? I am sure at some point, with married couple, they had to accept the issues that exist between them (at least back in the "ancient" days where divorce is not an option).

My grandparents were the perfect example of perpetual issues that never go away. They bicker all the time but when my grandmother passed away, my grandfather was so heartbroken.