Normal relationship issues vs. Non normal relationship issues

[Far Side Of the Moon]

I ask this because I'm aware in a relationship couples are going to argue ,disagree and not see eye to eye because its two different people trying to learn one another and how they operate, become one and function together..,so Of course there will be hiccups.

Now, my question is what are issues that fall outside the norm? ( in not talking about obvious ones like domestic violence, physical or verbal abuse....) what are some that may seem more subtle ( and would possibly be a make or break issue) that could be talked about here?

I hope I made sense
Thanks for posting