Not that I really mean to take Neil's side here or anything, but how do we know that comments he might have made to Nick about breaking up the band were really a "threat"? When Nick says that Neil "threatened" to end the band, it implies to me that he thought it was something said for spite. Maybe it's just what Neil was really feeling at the time. And maybe when he said those things he really meant them at the time he said them! People say they're going to do a of lot of things when they're stressed out - believe me, I know - a couple of times within the past few weeks I've nearly quit a job that I actually like for the most part. And when I was thinking I might quit, I MEANT it - but of course, then things calm down and you get over it and go on. But sometimes things get to a breaking point, so as for Neil eventually "pulling the pin," well, why was it Neil's responsibility to stay in a situation where he wasn't getting what he wanted anymore? It's not like he was married to Nick and Paul. Yes, maybe they were friends, but the band was likely to end at SOME POINT, as most bands do. I can see why Nick might take this personally, but we don't really know if it was meant that way when it all actually went down.
However, having said all that, I can certainly understand why Nick might might feel this way, and he's certainly entitled to his opinion about it. This sort of situation is fraught with emotional overtones, and while it's one thing for me to comment as a third party observer, I might feel very different about it if I was in Nick's shoes, and might very well feel exactly the same way he does. I don't think Nick should be crucified for making these comments - he's only human, after all, with feelings that can get hurt, just like the rest of us.