It's easy to pathologize what we consider bad behavior, but it's important to recognize unhappiness and our resistance to it. People who are abused, disrespected, or ignored take on behaviors that, on the one hand, can be viewed as pathologies and, on the other hand, serve as small acts of self-preservation. Drug use, lying, stealing, and irritability are all coping skills that enable one to resist or continue living when they may very well feel like giving up.
This may be a somewhat difficult idea to wrap one's mind around because of our tendency to place the locus of the problem within the other person rather than recognize that we play a part, especially in intimate relationships. It becomes harder to see that your partner's behavior may be in direct response to your treatment of them; your partner may act the way they do because of something you are doing, rather than tell you, they may act in ways that not only communicate their unhappiness but also carve out for them some way to resist and survive.
Before you go away mad, consider the opportunity this view offers. What if you could have a conversation with your partner about their unhappiness? Well, if you consider their behavior as negative and blame them the conversation will probably shut down before it begins. On the other hand, with the ability to discuss their behavior and take some responsibility for your part you could gain some valuable insight into how to increase not only their happiness but also your own. Their behavior is actually a strength: they are trying to survive in the relationship.
Nagging is not just nagging. Dishonesty is not just dishonesty. Irritability is not just irritability. Nagging, dishonesty, and irritability are all forms of protest, resistance and self-preservation. Rather than stepping stones on the path to divorce these behaviors can represent opportunities to communicate constructively, increase happiness, and create a more intimate relationship.
Empathy can enable you to adopt a new perspective because it will allow you to imagine the suffering of others. Their suffering is not an isolated occurrence but one that is directly related to your own suffering and how you treat them.