Six Feet Under
In July 2001 (the beginning of the second season), Nate learns that he has arteriovenous malformation (AVM), a potentially fatal brain condition which could cause him to have a seizure or stroke at any time. Nate has a very pronounced fear of death, causing him to initially hide the information from everyone around him in order to avoid admitting his very real chance of dying young to himself. Early in the season, he visits Seattle and seeks comfort from Lisa Kimmel, his "fuck-buddy" during much of his time there. He ends up cheating on Brenda with her, only adding to the subconscious pressure on him; worse, he has his first seizure while there. Additionally, several months after leaving Seattle, Lisa moves to Los Angeles and Nate learns that she is pregnant. Through the course of the season, however, Nate slowly becomes able to face his fear, and finally is able to tell his family about the condition and seek a high-risk surgical procedure as treatment for it; he is also able to tell Brenda about impregnating Lisa, but when it turns out that she had been cheating on him as well, they split up. The season ends on a cliffhanger, with Nate undergoing the high-risk surgical procedure required to save his life.
The third season begins on a surreal note, exploring various possible outcomes of Nate's surgery and his life, and then skips ahead in time to late 2002, where it is revealed that Nate and Lisa have married; their daughter, Maya, is three months old. Their relationship, however, is tumultuous, and just when things are beginning to look up for the couple, Lisa is reported missing, and a month later her drowned corpse is found. Nate is forced to deal with both Lisa's death and being a single parent for Maya for a time, but eventually he rekindles his relationship with Brenda, and the two become engaged for a second time, marrying six months later, in October 2004 (the beginning of the fifth and final season). Their wedding day, however, is darkened by Brenda's miscarriage the previous day.
Immediately afterwards, Nate suffers a brain hemorrhage from a second AVM that had developed since his mid-2002 surgery, and slips into a brief coma. He wakes up in the hospital the next day, and the doctors believe he will have a healthy recovery over the next few weeks. Brenda tells him that she forgives him for his adultery, but he responds by saying that he wants a divorce. Brenda leaves his bedside devastated. Nate is also visited by David, Claire, Rico and Maggie, but Ruth can't be reached due to being away on a camping trip. At the end of the day, Nate unexpectedly dies in his hospital bed while David is sleeping at his side.