#1 Forgetting to Be Friends
The root of a healthy relationship is friendship. Don’t let your romance (or lack thereof) make you forget that.
#2 Intentionally Saying Hurtful Things
This is a tactic that some people just didn’t grow out of after high school like they should have. Even when you are arguing with each other, don’t say things that you know will hurt them. Don’t disrespect them or say something that could affect them negatively.