What does it mean when he keeps pushing me away whenever he’s angry or sad, like he doesn’t allow me to be there for him?  He’s also never there for me when I emotionally need someone.

Sounds like this isn’t what you want … at all.

Let’s rephrase this question as a statement of your needs: “I want a partner that’s able to express his feelings directly to me, who will let me comfort him and hear him even when he’s not his best, and will comfort me and listen to me as I do for him.”

Write this as a letter and deliver it to him or say it directly to him when you are alone.

We can’t read his mind and neither can you. Hopefully this will spur him to disclose to you whatever’s up with him and/or to seek professional help to better deal with his emotions. If this doesn’t work, however, then you’ll probably need to establish a firm timeline on how much longer you’re going to put up with this.