Need help with player, 1st time DM
So, I don't know what I'm supposed to do and any help given here is much appreciated. English isn't my first language so I excuse any grammar problems.
First paragraph is kinda important,
skip the second paragraph for the backstory,
Third paragraph is more in depth about the problems
Fourth and last paragraph is the basic problems (just scroll)
I (16) started a DND group with my friends about like almost a year ago, we all go to the same school and are around the same age. We are 8 people, so I dm for 7 people most of the time, I know, a lot, but we agreed we would all try to work together and have a fun time, we also want this campaign to take several years if possible or just as long as possible, which is also why after about maybe 10ish months and like 12 sessions (hard to get sessions together with 8 people all in school, starting work and learning to drive) they are level 4.
I haven't given them a clear goal or anything they need to do, however, I know I railroaded the start a bit but everyone said that was okay. Overall, I made the world myself, the problem is that in short, the gods have lost access to the world which is why the world gets corrupted more and more. My players have multiple strings which they can play out, like the forest that surrounds them growing more aggressive, another adventurers group trying to sabotage them all the time, a bigger city gaining control and being a threat to the village they are in, the mayor not caring for the village and hating adventurers, his cousin creating a secret adventurers guild to tackle the problems in the village and make a better image for the village. And a few more but you get the jist, hopefully. Of course all of those problems and the characters personal backstory would lead to the bbeg, the person that took position of the gods.
Now, I went a bit wild and I'm sorry for this long block, but I think it's important for you to understand the problem that I have with the player. The player in question is the oldest one of us, being 18. Personally, I feel like I am a bit biased because the guy is two years older than me and has tried to hit on me several times, last a few days ago when he was drunk saying he would f me if I wasn't this young, little bit problematic but I mean, alright. He has often times said he doesn't like the way I dm, especially since he is a tiefling warlock, pact of the chain with a great old one, being a demon prince, and that I don't bring in his pact often enough (note, we have only had a few sessions when this started and he has been cutting himself every session, sacrificing his blood and asking for help from his patron for almost everything). We talked about this with one of the teachers at our school, since he's an experienced player and DM as he's played for 40 and Dm'd for 30 years. (Note, he went to the teacher and talked to him about all this and asking him to talk with me behind my back, before even mentioning it to me in person) We got to the conclusion that since he's only level 3, he's basically dust to a demon prince. After that in the next session, he jumped of the boat they were on for unfair treatment by the whole group (he wanted to blow up the reactor powering the ship). We solved that by saying he put on his boots of hovering earlier than everyone else. (Note, his idea was that I would make an arc all about him by making his patron save him dramatically and the next three sessions being all about him, idk how he wanted that to work out). His latest idea was in today's session, they found out another party was sacking in their glory and lying about having attacked and kidnapped them. One player attacked the leader of the rival party, which is "fine" since the leader was a rabbit and the player has always hated rabbits and he has been making up lies. He later said himself that he maybe shouldn't have done that and apologized to the rest of the players, which is why he didn't get any negative feedback from the others. However, this of course lowered the groups reputation. Later that day, the player this post is about asked a granny (the one who cared for the rabbit as he got hit by the players attack) where the other party lived, so he could visit them. After the granny made a rude remark about his group and that she knows that tieflings are always up to no good he dug his claws into her throat and started strangling her. The tavernkeeper and others saw this, he got promptly beat up, while that happened, the other players were trying to save their reputation and just looked dumfounded as he ruined all of their work. After that, a little time passed and while I played out another situation with another player, I heard him saying that it's just so unrealistic and that everyone in this village is overpowered since he was just beat up like that (note, remember, he's a pact of the chain 4th level warlock, the tavernkeeper grabbed him and beat him up, they know he's a half orc with an adventurers background , also something they could play out) literally everyone else is scared of the adventurers. I then stopped talking to the other person and turned to him, asking how TF he got that impression, he literally fought a half orc (note, the half orc grabbed him and pulled him away from the granny with a hit to the face, he then kept attacking the guy too) he said it was just a joke and I should chill out and I said "he should keep it down and if he's got problems to please talk to me about it after the session, as I've asked him multiple times to since he's always talking to others if he isn't on his phone, which is also something that we have told him to cut out cuz it's distracting us, as he isn't even quiet when he watches Instagram reels and always disturbs us too" he asked what else he is supposed to do when he isn't talked to. We talked a bit more and he then said that my campaign is just so railroaded and nothing they do has any impact on the story and they have nothing to do in the campaign. Another player got mad at him and told him that he quite literally just completely threw all their work in the trash, the others didn't say anything.
So, in general, my problem is that he is always disturbing and on his phone when he isn't entertained and that he keeps saying I don't care enough about his backstory, that all enemies he engages with are overpowered, that my story doesn't make any sense, nothing they do has any impact. Even in my friends campaign (the same player group, just her as a DM and me as a player) he has been a pretty hard player to work with. However, in the campaign we played with our teachers in school he seemed to be a good player, which is why when I asked my teachers for advice, they were pretty surprised when I told them about this. I just think I can't always run to them when I got a problem.
Any help is good and appreciated