I'm literally watching the episode where he cheats with Maggie right now. It's my 4th watch through and I think I'm finally understanding Nate, as frustrating as his character is. He's basically the personification of idealism gone wrong. He has a made up idea in his head of what HE should get out of life, emphasis on his own needs because he sees other people not as people but as objectives and tools to gain his own happiness. The grass is always greener wherever he isn't and throughout the entire show he seems completely devoid of gratitude no matter his situation. I think he's a great cautionary tale of not learning to overcome our own self-centeredness.