<human>: In a relationship, is it healthy to have issues that couples don't discuss, or should a couple be able to talk about anything, however trivial?

There are times when my(22 F) boyfriend (24M) of 2.5 years will clam up and not want to discuss an issue. For background, we have been dating seriously for a long time and constantly discuss marriage and children.

Some issues are trivial. For instance, he's a med school student. Today, when I told him "good luck with the studying", he said that he wished I wouldn't say that. He didn't want to discuss how his studying was going.

In other instances, he has clammed up when he has had a major issue like a fight with a friend or family member. When this has happened to me, he always wants to know what has happened and to listen. If I don't want to tell him, he'll keep asking until I do tell him. However, in his case, when I want to know, he won't say anything. He'll say things like, "There's nothing to tell" or "I don't want to talk about it." End of story. That's it. I might know that whatever it is is truly bothering him, but he just won't talk about some of those things. 

He also admits that he has had a double standard when it comes to this issue.

I want to know what is fair/appropriate for couples as far as sharing information. Should everything be open or is it alright to have issues that you refuse to discuss with your partner?

Can you summarize the given text in a few sentences?
<bot>: ! My boyfriend sometimes refuses to discuss both trivial and serious situations in his life, and I don't know if it is healthy for couples to have some topics they don't want to discuss with a partner.