Sometimes I think I'm over my issues with TOG2, and then something sets me off all over again.
I think one of the reasons the JoeNicky fight plotline still bugs me so much is this: For that sort of conflict - where we're expected to be more or less equally invested in and sympathetic to both characters, and where the mystery of why one or both of them seem to be acting inconsistently with what we'd expect of them isn't the point of the storyline - to be satisfying, we need to be able to understand both sides of it. We don't have to think they're both correct or equally justified or whatever, but we need to understand why they think they're right.
With the JoeNicky fight, there are actually two distinct conflicts, but the film only really shows us both sides of one of them.
Conflict 1 is the Booker issue. The group agreed on exile, Joe wants to keep in touch so as not to leave him alone. This part is clear enough motivation-wise - Nicky hasn't changed his mind since they made the original decision, he's still more hurt and angry about the betrayal than anything else, whereas Joe has reconsidered, he's now more concerned about Booker being all alone. Fine - regardless of who we may think is right, it's clear where they're both coming from.
Conflict 2 is the lying issue. Joe lies to Nicky, both by omission and explicitly, about his choices to stay in touch with Booker and go visit him despite the exile agreement. And this is where the problem comes in. It's obvious enough why Nicky is upset about this, but the film doesn't actually tell us why Joe made this choice - why he lied instead of telling Nicky what was going on. The closest we get is Joe's "Because I knew what you were going to say", but that's not actually an explanation.
So we're left to try to fill in the blanks about Joe's motivation, which could be fandom catnip if the different possibilities were fun or interesting... but, to me at least, they mostly aren't.
Why did Joe lie? Because...
Joe is a dumbass sitcom husband who doesn't respect Nicky enough to have a difficult conversation when he knows they're not on the same page? Eww, gross, no.
Nicky is so cold and rigid and vindictive that Joe was afraid to bring it up? Eww, gross, no.
Joe cares more about Booker's feelings than Nicky's? Eww, gross, no.
Joe never even thought about how Nicky would feel about being lied to, he just didn't want Andy to yell at him? Eww, gross, no.
This isn't abnormal, "do whatever you want without discussing it and fight about it later if it turns out you disagree" is actually how they always operate and we just didn't see them disagree before? Eww, gross, no.
Joe thought keeping the whole thing a secret was kinder to Nicky than putting him through the discussion? This is the only one I've been able to come up with that I don't completely hate, but it's not really satisfying or particularly interesting.
The writers didn't care about this enough to even consider that this was something they should've addressed? Almost certainly the real answer from a Doylist perspective, but again, not satisfying or interesting.