When you or the other person starts to make demands or ultimatums in a more adversarial way, look at those as clues to figure out what's really going on for yourself or the other person.
Go within yourself to find out what really needs to be said.
Relationships can lull you into complacency by the absence of negativity or complaint.
When you communicate with someone, there's generally a gap between what you say and what you're thinking.
When you find yourself disagreeing strongly, agree with as much as you can so you can initiate an affirming atmosphere.