I am playing with 2 players because no one else can, or wants to, play. One of the players feels like I target him. When he tries to do something that won't progress the game, I let him do it; if he fails, he then gets upset. I'll give you an example:
So the group was in a dungeon going against a hobgoblin captain and a group of 5 goblins. The hobgoblin makes a multiattack and rolls enough to hit and he wants to dodge the attack as a reaction. I don't know if that's possible. I looked it up; nothing in the Players Handbook, so then I say, "no you can't," because he already moved and used his action. But, he wants to look it up and he doesn't find anything; so, he is in a bad mood.
So, then the goblins try to make short bow attacks and his player is closer than 30ft and he says they can't attack because its below the minimum range. That makes no sense; if anything, it's a better chance to hit. I say whatever I don't care and keep the game moving. Then after the game I try to address it and tell him and he said that, "nope we're not gonna change it because you said it goes this way." Now I can't address him because he uses my words against me.
So, what do I do?
To all your answers: Okay so I've pretty much tried these and I'm taking a break currently letting us both take a break. Okay so I use D&D beyond and I asked some other DM and they told me what to do. So I show the player what they said and he still is defiant; I've looked up the rules showed him and he is still defiant. I'm thinking about just not playing with him but then I can't play because there would only be one player but thanks for all the possible solutions.