I know this thread is old but your situation is eerily similar to a situation like mine. I'm a Gemini woman though, but I believe I am qualified to answer.
How knowledgeable are you about natal charts? I'm saying maybe your Gemini is a typical Gemini in normal circumstances unless it comes to love. Since you say he's shy, he probably has a Venus in an introverted sign. Venus in a natal chart is how a person behaves in love. You can find out about this if you know his date of birth and place of birth. I would guess he either has a Venus in Taurus or Cancer based on your description of him. Maybe Cancer because he seems sensitive when it comes to love. Anyway, I will try my best to help you out but take my advice with a grain of salt because like I said, I'm not sure what his other signs are but he definitely will not behave like a Gemini in love.
I'm just going to go that he is sensitive when it comes to love. I don't know your Gemini's history but maybe he has had some issues in his past where love was not reciprocated well, that deeply hurt him, and so he emotionally shut down and retreated into his shell. He could very well have real feelings for you that he withholds because I know that typical Geminis display the symptoms you just mentioned when they are romantically attracted to someone.
But you said he started to become mean and you said you might have hurt him. If he is sensitive in love, expect him to withdraw until you somehow confessed to him or asked for his forgiveness if you know deep in your heart that you have done something that hurt him. I do think Geminis can be prideful but we are forgiving. If we sense that you are sincere with your actions, we will open back up with you. But if you keep dragging and dragging this confession that you're planning, the more you will build up resentment in him because he is probably waiting for you to make amends for the perceived wrongs that you've done (or that you actually did, since you are saying that you might have hurt him.)
What I'm saying is... if you really do care about him, and if he cares about you enough to be sweet and caring in spite the fact that you have hurt him, maybe the best way to end this conflict that you do have is to take the first step and talk to him about it. Geminis are communicators, we like to talk things through and we hate it when we're not being heard. So your non-response maybe a sign of rejection to him because you are refusing to communicate the truth of your feelings and clarify your emotions, and this makes him angrier since he's sensitive he can probably tell there's something you're hiding and he could imagine all sorts of scenarios until you clarify this with him.
So I suggest you reach out to him. If he truly cares then he will most likely respond. I mean there's nothing suspicious about texting asking what's up or maybe just catching up, right? The worst thing that could happen is he doesn't reply, but like I said, if you're coming from a sincere place, he will probably sense it and will respond.
Best of luck with your Gemini and have a great day.