I agree in principal, but there is one problem I have with the logic when I think about it. If there is more to know (again, there must be, even at a minimal level), why isn't Richie saying so?

Sure, he is locked into some legal agreement where he can't throw Jon under the bus. I get that, but does that legal agreement extend to Jon having carte blanche to throw Richie under the bus? I think not. If addiction was not the reason (let's say large percentile reason), then why is Richie simply not saying "hey, me falling to my addictions was not the reason I left, I can't delve into the reasons why, but it was not that?

I don't buy because he is the bigger/better man. You say they let us know what they want us to know. Ok, but why wouldn't Richie want us to know he was not off his tits and that caused his departure? Surely, if addiction was not the reason and Jon has (implicitly) said it was and David has (explicitly) said it was, that would be libelous if untrue.

So, while it seems obvious there are things at play we don't know about, it also seems obvious to me that addiction was the main reason Richie left. Remember, we are talking about that point in time. Perhaps Richie was moving towards the door anyway and was disenchanted in general. However, that precise moment he left seems to have been caused by addiction, unless Jon is lying and Richie is letting him.