I had one or two mostly longterm boyfriends before I married DH ten years ago. One thing I noticed about these unsucessful relationships, and others I see around me, is that most friction is caused by one or both people trying to change and control the others 'core' personality.
My DH drinks a fair amount of beer and does the bare minimum around the house which in the past would have annoyed the fk out of me, but because I've learned to accept these things as a part of him, we actually get on and like as well as love each other.
I'm not saying that it's possible for everyone to gel with their OH all the time, or talking about problems like DV, but if you don't accept how the other person is surely it's going to cause shit whenever you're together?
Is it just something that comes with age in that you just can't be arsed with all the small shit hassles anymore? Or do you just 'fit together' with some people better than others?