Understanding a emotional avoidant/stoic

Does anyone have any book recs either fiction or non fiction that can help me understand someone who bottles up emotions. I am the complete opposite I’ve always felt my emotions in a big way and talk about them cry them out etc. I’m definitely anxious and he’s avoidant. Looking for more than just attachment styles.

He is so stoic and never lets me know what’s going on in his head. He’s had a few friends die and I want to be able to understand him, help him grieve. And just be a better gf for him for any thing else that comes up. I’d like him to feel safe to be vulnerable with me.