AITA for crashing out on my player
So i was dm for my group of lifelong friends. We were playing 1st pathfinder with mythic rules and a bit of homebrew. Down the line i of course realised that was a big mistake, but my story will be focused on one of my players. For context - he was LE Thassilonian wizard who was reincarnated in intellect devourer( that was premise of campaing as i made custom races for everyone - doppelganger, mimic, centaur and etc ). All other players were Lawful as well, some were LN and some were LG, they made their own guild, and wizard wasnt in charge So from level 1 to 8 everything was somewhat normal.
We had agreement with him that at every timeskip i will allow him gather 3 corpses for him to use, but their CR musnt be higher than his level, and of course he cannot use undead, constructs and outsiders. The last one he didnt agree, so we made him custom magic item, so he can infiltrate bodies of outsiders, while they were unconcious. This was disaster. He soon found out about demon nabasu (CR 8) and asked me if he could use it. I knew about nabasu's growth mechanic in general, i didnt pay attention to it though, as it never occured to me how badly can it be abused if it was in players hand.
He didnt come up with this scheme at first but this what became his routine at some point - he bought planeshift scroll, lowers his saves via negative levels and started to use nabasus ability on random commoners. Growing in stats on par to CR 19 while being much much lower level. He became stronger than everobody else in group combined.
The culmination battle between players guild and their adversaries begins. It took me using four 15 level npc-bosses with extra mythic abilities to make the fight somewhat "fair". So with much effort his nabasu body was defeated, while these bosses were at their last breath. And then he explodes out of this body and symbol of pain that was written on his main body activates, making these bosses almost useless and easy prey for other PCS.
After that we have a talk, both in game( his party members in demon hunting guild didnt appreciate him using demon powers) and out of game, i tried to persuade not to use this body as it was too op. He agreed in game not to do it "while his boss can see him doing that", and out of game i really couldnt persuade him to stop doing this.
So on next session i said that in game many people were unhappy with wizards actions(as killing commoners with nabasus ability turned them into ghouls), paladins of Ioamadae, clierics of Pharasma, and many many diferent factions were demanding guild to stop wizard from using nabasu, and alas wizard said he will stop.
He said that only because he found another thing to abuse. He found Bloodmoney spell, and with the fact that he can drain money from bodies that he snatched, he started to use ogres, to make himeself army of his simulacrum as they were essentially free to make now. With that he had at least four of his clones with him at all time to heal him with wands, to fire additional fireballs etc. And at that point they reached level where he had access to Limited wish, which was essentially free for him as he had simulacrum cast Greater restoration on him to negate Bloodmoney penalty.
Then we started his arc, as he was wizard who came from the past, we started exploring his past home, and he and i came up with very cool dungeon for players to go. Then came the horror.
It was final room of dungeon. I made four custom monsters with unique styles of fighting and good teamwork. At that point he had 3 mythic abilities that we didnt understand how they supposed to work - thats my mistake i know. So one with this combo of abilities he could target up to 4 targets with spell that does work only on one target usually, while not using a spell slot but a mythic power which he can essentially infinitly use as his simulacrum can restore it to him. So he could infinetly spam 8th spells with 3 additional tagets. He used greater invisibility and mind blank on all party, so even true sight can not detect them , and then he used Polymorh any object on all four of enemys, half of them became useless mice, other two were useless against invisible PCs. So he almost instakilled encounter that i was making for several weeks.
I was destroyed deep down, but we kept going. Next battle was with one of Runelords - Sorshen, who was wizards superior back in the day, so i prepared whole dialogue between them before the fight, with options to become allies or skip the fight. Then i start narrating her part of dialoge, wizard said - were invisible she doesnt know were here, we ambush her.
This was my breaking point, i crashed out and start to violently kick my closet, as all my players were stunned. i fell on my chair and sit silent for 5 minutes, then i apologised and i were continued session, it wasnt long before we finished it anyway.
In the end i nerfed his Blood money exploit, reread his abilities and we sit down to talk how they intended to work, so he didnt have acces to infinite spells anymore. We made up and still play together, but i banned him to play spellcaster in serious campaing for a while.
Edit: Thank you everyone for your comments. I appreciate it i really do. After this incedent i talked a lot with my friends and close acquaintances about it. Yes i could have done a lot to prevent all of this, now i look back and see it. I shared this story here to see if i really learned my lesson with this - turns out i couldve learn more - as some comments put this situation in a new light for me, i hope i can improve and grow from these mistakes.