So just fyi I watched all of season 5 in one day and I am still not totally sure if I have processed even half of it, but like lets get into it.
So SPOILERS in the next part, so QUICK scroll away!
So, ok.
We start out the season strong after learning that Amber died while picking up House from drinking, and because of that, Wilson leaves and tells House that he thinks "They were never really friends,"
House is already going down a dark path of guilt ever since Amber died and has since been drowning in it. But, because this was "technically not his fault" he continues to tell himself such.
Now I don't remember if it was this season or last season when foreteen becomes a thing, but like yeah.
Taub has that whole thing prior to Kutner about how suicide is selfish and terrible and he reveals that he did in fact attempt suicide in med school.
We see that Kutner starts to decline nearing the end, now yes I understand that Kutner was technically written off because Kal Penn was offered a job in the Whitehouse (thanks obama), but lets analyze this as a whole. Kutner, being one of the prime characters that everyone compares to House. One of the characters that is supposed to have an element that most anyone can relate to, a character with a tragic backstory and a reason for how he acts. Another character that acts like House but for different reasons. Kutner at his core, is an enigma that I suppose we as watchers were supposed to unfurl as the show went on. However, we all know that his time was cut short. And I think that in itself this was an accurate representation of what suicide can look like. As someone who has been suicidal and attempted before, what I can say is that most of the time for me, it was on impulse it was at a random time because something set me off. And for Kutner I think it was honestly the fact that he was constantly compared to House (alongside many other things). Imagine that you were an adopted brown person into a white family after watching your bio parents be brutally murdered. You spend your life with an already complex understanding (or lack thereof) of your identity and personality as a whole. We see that Kutner has always had trouble with that (the bullying as an example) and how he is very frequently connecting with patients who he believed were in similar situations that he had been in. Like many kids who had to grow up too fast, Kutner now in his late 20s is just now discovering this ideation of what it means to be a child/have free will. And with this, we see this personality that comes of it, and his lack of understanding of what that looks like. We see him finally taking accountability of his bullying after years (which could also be interpreted as making ammends) and how when the patient tells him he is really not a "people person,"
Kutner's identity his whole life has been practically decided for him, whether it be being adopted into a white family, growing up too fast, being a bully, not being a "people person," or the most prevalent in the show being like House. While House's character and personality is a complex one and romantized one at most, he is a genuinely miserable person who has the goal of making everyone around him miserable as well (whether that be subconsciously or not) House is one of the most complicated and complex people I have ever seen. He is portrayed by himself mostly as someone who is only there to solve puzzles, an apathetic "monster," someone with no morals, etc. And we as viewers are constantly reminded of this in many ways, such as his treatment of patients, Cuddy, Wilson, etc. but we also get to see his more soft and human side. Which the team very rarely sees, given that he hides that from his employees and is also their authority. If anything, constantly being compared to House was something that one could only assume would start to chip away at you especially if there was truth in it. Take foreman for an example, he tried so hard not to be like house, not to be what he feared most, and that was losing his morals, aka becoming what he perceives as house. Then take Kutner, Kutner his entire life has been put into boxes never truly getting a chance to properly form his own identity, and that eventually builds and builds. And I think that from his last case, or something along the lines of it, he discovered that he was too much like house, or that his attempts that finding his own identity were futile. Kutner has a deep rooted unsolved trauma that effected him in his everyday life no matter what he did. And in spite of that and because of it, he acted the way he did, for better or for worse. And all in all, they had to kill of Kutner not only because Kal Penn's job, but also because they could start to humanize and change House's destructive path or at least divert it a little bit.
Kutner and Amber died for House's character development, which is why when House starts to go down an even deeper and darker spiral of guilt after Kutner dies the episodes start getting even more House-centric. This season we saw more human sides of house than we have ever seen before, and we also see what that does to him. Whether that be the methadone arc, or the flagrant disregard for his life, and of course the hallucinations. Kutner's death effected House in such a deep way that he started taking so much valium that along side his sleep deprivation caused his guilt to surface from repression and give him actual hallucinations. Amber being the one he had repressed for too long, Amber being the dominoe that started this whole clusterfuck.
Then of course we have the nightmare (hallucination) that was the last 2 episodes of the season, wherein the lipstick and Cuddy were both being used as metaphors for his own dependency and addiction. Along with the case that argues his "split brain" one side, the creative side making the hallucination telling him that be should become clean and sober and using Cuddy as an example for that. But then the otherside taking cuddy and her lipstick and using it as a metaphor for his obsession. In this season we see House's everything decline as his world falls apart, Cuddy, Wilson, his team, his dad, everything and then we finally see him snap.
House going to rehab what arguably the overarching point of this season, the point being that they slowly send him down a descending path, and then when he gets to the final step he does something, the one thing he can do, which is admit himself to rehab and admit he has an issue. Amber, Wilson, his dad, Kutner, Cuddy, and the hallucination was a wake up call for him and even he knew that early on, hence the one meeting with his psychiatrist. Even then, he knew he needed help. And his breaking point, was seeing Kutner and realizing all of his growth, his whole perception of his "life story" and character development was fake was his last straw.
House finally broke, and that was this season's point. House's pain and guilt finally winning him over, and eventually breaking him.