First of all, everyone in the game is entitled to have fun. That’s why it’s a game. If you weren’t having fun, you wouldn’t be playing.
That applies to the rogue as well as anyone else, but ultimately the odd-man-out who is causing problems for everyone else is more wrong than a group that’s otherwise enjoying themselves.
You have to accept, first, though, that the correct answer to the situation may be not playing together. Friends don’t always all want the same thing from a game. I certainly have a few close friends I nonetheless have decided to not play with (and vice versa); the things we want from the game are too different.
For example, someone who constantly wants to go off and do their own thing away from the party, and has personality/alignment conflicts that they do nothing to alleviate and cause problems for the party and make the campaign difficult to continue? That’s the kind of person I would choose not to play with. And I know people like that who would not play with a group that would stop them from doing that. I know others willing to compromise. You need to know where your group stands.
A good place to start, often recommended here, is the same page tool. Using this can give your group a better idea of what everyone wants from the game.
It may be that you are all on the same page, and the rogue player is just better at it. Or it may be that the rogue player and other players want very different things from the game, that the others don’t want characters at the level of competence that the rogue has (or, at least, don’t want to invest in mechanical rules-knowledge sufficiently to create such characters). I’ll address both.
The rest of the group wants, or at least is willing, to get better?
Have the rogue player assist the others, the DM too perhaps, with how to optimize their characters better. Ultimately, this rogue? Really not that optimal. An adamantine weapon is a pretty common tool for mid-to-high-level adventurers, and Agile Riposte is not a good feat at all. For that matter, the rogue is a pretty mediocre class.
So you can potentially catch up to this rogue pretty well if you are so inclined. As DM, favor intelligent, magical enemies, and this rogue will have little response. His Will is probably poor and his Fort is likely little better. For that matter, for all he’ll have above-average touch AC, it still probably won’t be all that good. If you bring heavy magic, particularly on reasonably tough chassis (like, say, a dragon), you may very well overwhelm this rogue, it might be too much.
The rest of the group is not interested in keeping up with the rogue?
This is where you have to start compromising, or agreeing to disagree and play separate games. Lay down some houserules for limiting power; it’s best if you can establish a good baseline of what you expect rather than saying “I’ll know it when I see it”—that’s probably not fair to the rogue player (personally, I probably would walk rather than try to play that particular guessing game). But that can also be really difficult to articulate, especially when new to the game. You don’t necessarily know what is or isn’t powerful (e.g. this rogue, who isn’t all that powerful at all in the grand scheme of things, but seems that way from your perspective), so you can’t accurately describe the power level you want.
Alternatively, you lay down your concerns and problems, and decide whether or not you can trust the rogue player to get along better. Don’t be intimidated by his supposedly-superior experience—his rogue isn’t actually that well-built and his behavior with leaving the party and causing alignment headaches implies, at least to me, a certain amount of immaturity. His experience, whatever it is or isn’t, doesn’t entitle him to dictate the game to everyone else, and it definitely doesn’t entitle him to have his fun at everyone else’s expense.