I don't think it's as black and white as you're trying to make it. Going to therapy means making yourself vulnerable, which is hard for most people and especially hard for some men. Telling someone that you're seeing a therapist means not only making yourself vulnerable in that moment, but also admitting to vulnerability and that you're exploring that with someone. It's a very personal thing, and even in a relationship, people are allowed to hold some things private. He told you when he was ready - and you got angry instead of thanking him for sharing that. Instead of a positive reaction, he got a negative one. For someone that is used to hiding emotions and struggles with being vulnerable, getting that kind of reaction basically says "this person isn't safe to share things with" and it encourages keeping secrets. It doesn't mean he's naturally a liar, it means he doesn't feel safe sharing thing.

I don't think it's as black and white as just he's honest or he's a liar. Is keeping something private being dishonest? Is sharing something when you feel ready, rather than when someone else expects to hear it being dishonest? Is it a lie to choose not to share something because you know it will not be received in a positive manner? Just something to think about.