The good news is that you both recognize this problem and are not in denial about it, so you’re on the same page. That’s always important in being able to address a challenge. Commend yourself for your honesty about your trust issues. And if you didn’t see them as trust issues, that’s what they are. You don’t trust him with your feelings because you are afraid that he will disappoint you or hurt you based on your past experiences.
For your boyfriend: Ask him to please be very patient with you. If he demands and begs that you be different than you are right now, it’s too much pressure for you to succeed. His best bet is to be patient with you and to give you positive reinforcement. In other words, if he can acknowledge when you do let him in, even if it’s something very minor, he will build your trust slowly but surely. But he has to be patient and not make demands.
For you: Break down your feelings of fear when you are in them. If you are very emotional about something, acknowledge your feelings and be aware of your fear of sharing that feeling with your boyfriend. Imagine what would happen if you did share your feelings, and tell your boyfriend, “I’m afraid if I tell you about what’s going on with me today, you’re going to ignore me, or belittle my feelings or break up with me,” or whatever it is that you’re afraid of. Then ask him if he can just listen to you and only say, “I understand.” Ask him not to try to “fix” the feelings you’re having but instead, to just be a listener who is supportive. He can hold your hand and hug you, but he can’t offer his own opinion — yet.
When you are able to do that, he should thank you for making that small step. It’s with these small steps that you’ll eventually take bigger strides in trust.
After months of his being a good listener and you being a sharing girlfriend, you can begin to ask him for more help if you want it. You can ask him for his opinions or his own feelings on hearing yours. And remember, you don’t have to be a victim and you don’t have to put up walls. You can stop him if things get too difficult for you by saying, “When you say that, I feel really hurt.” And then you can tell him why.
Hope that helps!