Quite some time ago, while watching tv, a couple from the taiwan show biz was being interviewed bout their long lasting relationship. And they shared their "secret". Decided to post bout it now before I forget bout them as I think it's a very helpful reminder.
If I remember clearly it has 4 NOs.

1. 不要有隔夜仇- No overnight quarrel. Whatever they are quarreling, they will have to settle it before the clock strikes 12 midnight. So after that, they won't be still harping on the topic or start cold wars.

2. 不要提祖宗十八代- No mentioning of other people eg. family or friends into the quarrel. Eg. Not to say things like, why are you acting just like your father, mother, friends, etc.... Not a nice thing to say bout this bout your partner's friends and disrespectful to your in-laws, which without them, you won't be with your wonderful partner.

3. 不把家丑外扬- No telling other people of the quarrel or family issues. Well, in case the issue has already been settled and one fine day someone came by and ask you bout that issue again cuz he heard so and so say something, then maybe another quarrel will emerge out of it.

4. 不提成年往事- No talking bout the unhappy past. Why remember unhappy incidents? Why remember what he/she did in her previous relationship? MOVE ON!

I can't really remember the exact words they use, but the meaning they want to bring across is here. For a person like me who has a super-duper-power memory storage system in my brain, I guess I'll have to work hard on point 4.