To me the fact that he worries you will "get mad" if he shares what he is thinking or feeling tells me that he doesn't feel safe sharing with you. Why is that? Do you get angry when what he is trying to share doesn't align with your thoughts and feelings? How are you two supposed to reach a point of mutual understanding if you can't initially accept where he is coming from? How is your relationship supposed to grow if you can't acknowledge that his thoughts and feelings are just as valid as your own?
If you want someone to trust you with their heart and innermost thoughts, then you have to be trustworthy - that means listening with compassion and non-judgement, and then discussing calmly and objectively. It's a skill, like any other, that can be learned.