I get the worries because Aaron not believing the John stuff was similarly exhausting but ultimately Robert has decided to get rid of Kev because of the risk he poses to Aaron and himself but mostly Aaron. That’s the bottom line, his guilt did trip him up of course but his fear for Aaron outweighed and tbh I think he knew something like that needed to happen that’s why he went to see Aaron.
How I think of it is, with the Kev/John parallels.
So like Robert vs John, Robert was the outsider perspective right? Like John had spent months manipulating the village up to that point to set himself on a pedestal, so when Robert came along he was able to see John Wasnt Quite Right, but he's the Outsider and the Insiders didn't want to believe it until it all went to shit, because their perspective was warped by the manipulations.
Flip that around and now Robert's the Insider with Kev, and the village are the Outsiders. Robert spent years with the guy in very intense circumstances, knows he was in for armed robbery (which, I just remembered, Kev said he was framed for!), knows that Kev said he was wealthy (which I don't believe was ever true: Kev clocked Robert's interest in that early on and I think used it as more bait, see how he got Robert back onside today by saying it'd been taken from him). He knows Kev got stabbed for him, and that he's responsible for it.
So now you've got the villagers with an objective Outsider perspective and they're all obviously like "uhhhhhh". But Robert being the Insider has had his perception warped and can't see it and defends him.
But THEN you bring Aaron into it, who's always been able to get Robert's head together. When Robert scoffed at Kev doing the robbery, it wasn't because he thought Kev's not capable, he literally said "why would he risk going back inside when he's loaded", so Aaron got him together and pointed out that neither he nor Charles have actually seen this money, which prompted Robert to confront Kev about it and expose the first lie (which again, Kev once again spun around with his explanation). But the bigger lie (and the biggest) still exist and so yeah he faltered when Aaron suggested getting him locked back up (because again, warped Insider) but he still agreed to do it anyway.
And so we wait for Robert to find out he isn't actually dying and hopefully takes this guilt off him (and again, he NEEDS to find out about the stabbing).