Attention is what will matter the most.  Actions speak louder than words so anything you can do that will make him feel special.  Call him on the phone just to say hi as many times as you can.  Tell him how much you love him and how sorry you are that you took your frustrations out on him.  Tell him he is so special to you and you couldn't imagine going on without him.  If he loves you back he will understand.  good luck