Hi there... I'm really hoping this doesn't sound harsh to you, because my intention is really not to diminish what you're feeling. I would however like to contextualise it a little...

There are about a hundred reasons he could have for not getting back to you, other than him being mad at you. Possibly, he's awkward, or he's busy, or he's having a tough time with something else. That he is mad at you is one possibility that is now, in your mind, a story that is clearly causing some anxiety. To me it seems as though when you do not hear from him, you feel anxious and stressed, and would really like some communication?

Now, you've already written to him and asked him to let you know. So I would really suggest that you acknowledge that you're feeling annoyed and anxious, and look at your need for communication (just,... accept that you need this, and accept also that it's, regrettably, not happening) and let it go.

Also: If he's mad at you, he's an adult and can communicate it. If he does not, that's his choice too. You've done nothing wrong. In fact, you tried to communicate with him. So there - you've done all you could. Now just... let it go.

Sorry if this sounds harsh. Hope everything works out.

Love and hugs!