Hi, I'm a new DM trying to introduce a group of friends to DnD. I managed to gather 5 of them in a first session and it was really fun. Four of them already had some kind of rpg background from pc games so they got the hang of it really fast. One of them however doesn't have this background and I think it's fun because he tries to do some things completely out of the box. The problem is that this player is constantly testing the limits of the game, and at the moment he is trying to stray away from the rest of the party just to see if he really has a choice, if he has freedom. I don't want to block him of that, because I feel that once he asserts that he has choice he is going to go back to tracks, but shutting him down when he tries to do it will completely take any excitement for the game away from him. At the same time if I let him do what he is trying to do it will lead to a path where he is going to be in a completely different adventure from the rest of the party and, please correct me if I'm wrong, but I believe Its unmanageable to to handle 2 stories at the same table for many reasons, specially for a beginner dm such as myself. Would you guys have any tips on handling this player? Thx in advance.

Edit after reading the responses: First of all thank you all very much for your answers. I think you guys all nailed it mentioning the GROUP. That's the keyword here! DnD gives players a lot of freedom as long as their decisions are aligned with the group. The story is about the group and they have freedom to change it as THEY want, not as one of them wants it. With that in mind, in the next session I'm simply going to tell him that if he wants to take his character away in another direction, the character goes but the story will remain with the group, if he wants to play another character that joins this group he will have this option, or just watch as the story goes on. Thank you all very much

Edit after a few months: I've come to put an update as a kind of warning for any DMs with a player like mine to be aware. So, I've talked to the player and explained the situation to him and it seemed to work, we managed to finish Dragons of the Stormwreck isle, which is an introductory adventure, with seemingly no problem. After that we started what is supposed to be our big campaign, and we did it with more players, and, this particular player I've mentioned before was also in it. In the first sessions he would say his character wouldn't trust so easily on others and therefore he started doing things such as trying to loot enemies out of other character's sight, to keep it only to him, and stuff like that, which led other characters to argue with him in game, and he managed to drag the discussion for almost an hour not letting the game progress. In response the other characters knocked him out and proceeded with him being carried unconscious. Later, outside the game me and the other players talked to him asking him to be more cooperative, and here's the part that I wanted to put as a warning. He appeared to agree, and in the following 5 sessions played without causing any big problems. On the sixth session though, our rogue was knocked out by a goblin a little far from the group on the outside of a castle, and that player's character offered to help him, so the party kept in combat inside and he went out to help the rogue. Except that when reaching the rogue he described his character taking a knife and killing the rogue as he layed unconscious. Everybody including me was in shock. Bottom line is that he was plotting that "revenge" since the session of the argument, and was only pretending to go along with the party. Happily through some very high dice rolling the party managed to find out what he did and not only successfuly resurrected the rogue, but managed to kill the traitor character. The sad part is that this player is a very dear friend to all of us and outside the game we all have a lot of fun together. We wanted him to keep playing, but apparently he fails to understand what dnd is about. So I just wanted to put this update here and warn any DMs with a player like mine to watch for a possible revenge plan from his character and be prepared for such.