Very tough subject IMO. I had a gf who would do the same and it is so mentally draining when the person you just want to be happy or at least not feeling negative won’t open up and let you know what’s up. In saying that tho I do really think you should give him the space he needs on this topic. Let him know you are there for him and he can talk to you about it if he wants to but otherwise don’t push it. When everything is okay if you think it’s not too much definitely have a talk about opening up and the stress it can cause when he shuts you out like he did, try and let him know because that isn’t okay. In certain situations it can be really really manipulative when someone shuts the other out and they know how it makes them feel.