Hi Serenity
I want to help, don't know if I can, but I'll try. Like you, I've had low self-esteem and communication problems. I was always uncomfortable, especially in SO relations and the fear of losing my best friend was regular. We get into these things hoping to find an understanding friend and instead spend hours dreading all the things that can go wrong
If your b/f is really trying to help, take little steps. Share one thing. Likely it won't explain everything and he'll ask for more. Go on until you feel you can't go further. Tell him it's all you can share right now because of your difficulty trusting, but that you're working on it and need his understanding. Hopefully he will allow you to work on it in your own way and the trust and understanding that develops will make you a stronger couple. In time, let a little more out each time. Try not to judge his actions or reactions as judgments of you. Like anyone, he has to process things in his way and he's probably not any more perfect than the rest of us. When we put ourselves out there, we take a chance that others will reject what they see. It doesn't always mean we are wrong. It may mean the other person has a difficulty understanding us. If they truly care and the relationship is important to them, they will be willing to reach a little further, thereby expanding their own knowledge and understanding and growing. If he is the sort who already knows everything and only points out where you are wrong, rather than learning with you, consider whether the relationship is right for you at this time when you are trying to grow.
I think honesty and the ability to be ourselves in a relationship is essential to true happiness. If we have to hide or pretend, we are always afraid of being "found out" for who we really are. It's easier and better in the long run to just be yourself from the beginning

"Our greatest glory is not in never falling, but rising every time we fall." Confucius