I have cut someone (in fact 2 people) out of my life because the relationship became very stressful for me because of the persons constant problems (a chaotic/drama-filled life going nowhere combined with lots of mental health problems).
The story of the second friend:
For a very long time (literally years!) I really tried to be very supportive, tolerant & understanding of his problems. But there was no real improvement in his life, and that as a figure in my life, he was a near-constant source of concern/worry/frustration/drama/general stress and anxiety (for example over the years there were so many times that I genuinely worried that he might kill himself, that he might harm others or that he would end up in prison etc).
This in itself might still not have been enough for me to call it quits on the relationship. But after a while I began to come to the increasingly unavoidable conclusion that as much as he suffered, there was no real genuine will on his part to really help himself be any better (and a lot of people tried to help him over the years!).
This was particularly illustrated in the months running up to me falling out with him for good:
He was always wanting my advice on matters, and yet he increasingly couldn't take any opinions that could be construed as personal criticism. However there were a lot of things he was doing wrong, and so some disagreement opinions was going to be inevitable (and this led to argument). His temper could be explosive, and sometimes he seemed to positively enjoy arguing (venting his emotions through argument etc). The arguments were so exhausting, I did seriously consider many times either just telling him what he wanted to hear, or avoiding contact with him completely. However by this point in his life, most people had abandoned him, and so being one of the last people left in his life, I felt a sort of moral responsibility over him (feeling that as difficult as it was, it was important for me to try and be a voice of reason in his life).
There were certain things that topics that I wouldn't budge on, such as his addiction to smoking weed: It was doing his mental health no good. But my refusal to condone his weed smoking (particularly when he started going on about having children with his girlfriend in his very troubled relationship with her) increasingly infuriated him.
One day he brought up the weed subject yet again, and when I (unsurprisingly) disagreed with him for the umpteenth time, his temper suddenly exploded, and over the next few days, he subjected me to a lot of verbal abuse and threats, and even went so far as trying to take "revenge" on me (for literally no more than me saying that he should try to quit weed before he tried for children!) by isolating me from other people by telling outrageous lies about me to people we both knew (luckily for me they saw through his nasty attempts to manipulate, but even so...It was a whole new low for him).
We had had some pretty bad arguments before, but his reaction to this one was on a completely other level!!
For me, this was all too much (and I vowed to quit contact with him).
He caused me a significant amount of stress.
However after a number of months, we bumped into each other and we managed to have a pretty civilized sit down discussion about what had happened. He appeared to be remorseful, and he said that he wanted to be friends with me again. He wanted another chance...I was reluctant to agree, but as we had known each other for so long (friends for 10+ years), I gave him one last chance. And the chance came with the strict requirement of "no more lies, no more BS. No more threatening behaviour. Ever!". I told him that while I would do my best to wipe the slate clean (forgiving his past transgressions), it was only on the condition that he made a concerted effort to get his act together (as fundamentally, the friendship had been in long decline for a number of reasons before the big falling out had occurred). I told him that I would do my best to be supportive of him, but that he had to change.
He agreed to this, however almost immediately. he lied to me.
I stupidly overlooked it (giving him far more benefit of the doubt than I should have given him).
A few months later, we had a blazing argument (though not nearly quite so severe) about his racism and a previous lie (which although I had tried to forgive him, had been so bad that I had struggled to forgive him and needed him to be honest about it).
But still I gave him another chance (fool that I was).
But not long after that, after one fateful visit I quit contact with him for good. There was no big blowout argument, no dramatic climax etc. Instead, observing his behaviour and listening to the things he wanted to talk about (politics, always politics) as he chatted away, I realized how completely unchanging he was.
I think that in reality, friendships can often suffer & survive many transgressions. However if a friend has become a negative figure in your life (one who you associate more with stress & anxiety etc than of good times and happy memories etc) and you don't see any genuine will in them to change for the better, then that really is a friendship killer. As long as there is hope, things can improve (but no hope and things will come to an abrupt end). And there doesn't need to be an argument (any great falling out) for this conclusion to be suddenly realized.
Initially I had forgiven my friend because quite frankly, as badly as he had behaved, I was going through a very tough time and I was still clinging onto the hope that things could return back to how they were in the past. And I thought that in him regretting how he had screwed things up, he would relish the chance to make things work again. But the problem is that he simply wanted to go back to before (and before wasn't good enough for me). The argument may have been a turning point (a hastening towards the end) in the friendship, but it was his prolonged mental health problems, antisocial attitudes and lack of genuine will to get his act together that really caused me to not want to associate with him anymore.
He caused me so much stress over the years, that as much as I felt bad for him, coming to the conclusion that I was better off without him in my life, was ultimately inevitable.
Since quitting contact with him: I do admittedly still occasionally worry about him, especially knowing that when I cut off contact with him, I was one of the last remaining people in his life (and his mental health had been in very concerning decline).
So the end of the friendship was not an automatic end to the stress/anxiety that he caused me.
But I am definitely better off without him (and a handful attempts on his part to contact me since, have only illustrated how much he brings nothing but stress/drama into my life whenever he has any contact with me). So I know I made the right decision (with it being more and more reinforced the longer I have stuck to my guns on the matter)
And as time has gone by, I do actually think and worry about him increasingly less, finally genuinely feeling now that he (and whatever happens to him) really isn't my responsibility.
By getting rid of such a negative figure in my life, I have in turn valued my own life and happiness a great deal more. Less preoccupied with worrying myself about him, I have suddenly had so much more mental energy to devote to my own life.