Hi Chloe,
Some people are very reticent about deep stuff, especially emotions.
One practical thing you can do is to be with your boyfriend and not push him to talk about anything that's hard for him.
It might take a long time, but if you listen to what he talks about, and don't push for anything, you will start to get a feel for the way he is thinking. It's a real skill, and hard to do, but just being there and paying attention is the key.
I learned this in my teaching job, and I was amazed at the revelations that come out when somebody starts to let down the barriers. It was never what I expected, but it was always good to see someone loosen up.
I hope that helps a little.
Cheers, Myzen