I'm currently 9 sessions in to a brand new 5e homebrew campaign, with a greatly varied party of six players; two newbies, two intermediate players, one very chill wringer veteran, and my previous Pathfinder DM, who is about as new to the 5e system as I am. He's DM'ed for me in three previous short term campaigns, and he's a decent DM with a tendency towards railroading. This is also my first time DMing.
I've been having trouble establishing a good rapport with him as a player in this reversal of roles. He has a tendency to rules-lawyer, which I've tried to call him out on subtly, but the biggest issue is how he's treating my other players.
He's playing a NE rogue arcane trickster who is secretive, manipulative and likes to split off from the party if they cant solve a problem by themselves. This leads to very overt sighs and grumbles when I'm doing a scene with the rest of my players. I'm trying to make the world a good balance between sandbox and storyline, but this player is trying to shotgun the story (i.e. jumping headfirst into deep story progression without taking time to explore or let other players catch up), which is making my new players, who are still exploring the mechanics of the game, kind of lost and uncomfortable.
When he's not doing that, he's bullying other players into making skill checks to gain knowledge that he wouldn't have previously had, and just generally gives off a sense of displeasure that he can't get away with lawless mayhem and thievery, even if he fails the appropriate checks I ask of him, and seems annoyed when my NPCs become realistically distrustful and hostile.
I don't want to kick him from the group; we've been friends for years, and I genuinely do like his character's potential, but I greatly dislike feeling undermined in my authority as a DM, and the feeling that my other players' fun is being stepped on. I need to to talk to him about this, so do y'all have any advice on what I should bring up as suggestions for a change in behavior? Because I don't think in-game subtlety is going to hack it for much longer.