Your introvert isn't like you. He has a finite amount of emotional energy to spend on things like being with other people. He still has to spend these 'social calories' doing mundane things, like chatting, answering questions or just interacting.
Your introvert doesn't hate you. He just has a good sense of how much social energy he has left. He's been an introvert for all of his life and has learned what he can and can't handle. He's going to want to try to find space for himself when he feels his limits are getting close. That might mean he has to draw boundaries and force separations that you don't understand. He's sorry about that.
Your introvert will do his best to be social and if he's had a chance to recharge recently, he may really enjoy it. If he hasn't had a chance to recharge though, he may find being so very stressful. This is not him being a big baby. This is him fighting hard to not disappoint you while something inside him is screaming for mercy.
Your introvert totally gets that you don't understand how his brain functions. It's a source of endless frustration to him, but he tries to be understanding with people who seem to have endless amounts of social calories to spend. He also realises that he doesn't really understand how your brain functions either. He knows it isn't your fault that you think he's making a big deal over nothing when he says he needs some space. But please understand, no, he really does need that space. It's not an option for him to keep on being social. You need to think of your introvert like a can of coffee. Each social act he takes drains off a layer of ground coffee. When you reach the bottom of the coffee can, there's no more coffee left to give.
Your introvert probably really enjoys being social. Him being an introvert doesn't mean that he wants to be a hermit all day, every day.
Yes, your introvert gets emotional. He often gets emotional because he has an empty coffee can. He'll be just fine if you can let him recharge his batteries. He may act weird when he's emotional. That's because he may actually be panicking inside. Don't make your introvert panic. It's not good for him.
Your introvert is a person, just like you. Be good to him and he'll be good to you.