I think that you are very close to understanding why you bite your tongue with your guy.
You gave an important clue when you said, 'I don't know how he really feels about me.' What your sentence is telling us is that you are afraid to open admit to liking him before you know how he feels about you.
In short, your silence is an unconscious defense mechansim, a way of protecting you from painful feelings of hurt, rejection, humiliation, and so on. The problem with defense mechanisms is that they often bite you in the butt.
You see, your silence makes you less appealing, so your worst fear may very well come true. He may become disinterested in you, which means you will feel all the hurt, rejection and humiliation that your silence is supposed to protect you from! What can you do?
Instead of silencing yourself across the board, be selective in what you say. Tell him your thoughts and feelings on all kinds of safer topics. Also ask him questions about himself, his history, his likes and dislikes. Get him talking about his favorite subject--himself.
Humans are always drawn to people who show interest in them. When you feel safer, gradually move into telling him what you like about him. It is normal to tell a friend what traits you find appealing, so why wouldn't you give your boyfriend the same fine treatment?
Again, humans are endeared to people who admire them and let them know about it. As you open your heart and tell him what is great and wonderful about him, forget about yourself. Your ego isn't at stake here at all.
When you tell him what is delightful about him, you are not asking for a lifetime commitment or marriage, you are just telling him about himself. In other words, you don't risk rejection or humiliation by opening your heart and describing his fine traits.
By speaking from the heart, without asking him for any emotional declarations in return, he will grow fonder and fonder of you, and soon he will be telling you what he likes about you.
Love is like a tennis game. Serve the ball, and he will bounce it back. Let me know how you do.