Is it a guy thing or?

My bf and I live together, and have been together for several years now so we know each other pretty damn well. Not often, but sometimes he’ll come home from work and I can tell stuff is on his mind, or that he’s had a bad day. I ask him what’s wrong and he’ll say “had a bad day” or “nothing”. But I can tell it IS something. Then the next day, he’ll apologize for being in a “mood”, let me know it’s not me or anything I’m doing, just that sometimes “life” gets to him and he gets a little frustrated. I know his feelings and I have those days too, but I’m a little different in the way that I’ll open right up and say what’s on my mind and WHY I’m having a sh*tty day. He isn’t like that and it bothers me. Do I just leave him alone and let him stew in that?? I would rather he talk to me, tell me what he’s stressed about, and who knows? Maybe I can either help him with what he needs/what’s bothering him or at the very least lend an ear so he can vent. I don’t want to be intrusive, I just care, and I know holding stuff in isn’t healthy or good either.