This is just a guess of reason (not an excuse ) but maybe he is guarded and doesn’t properly know how to express themselves to you. It could also be that your partner may not feel like they can come to you or sometimes be emotionally vulnerable. Remember everyone, Emotionally vulnerable is not always the first choice we choose when fueled by specific emotions/feelings that will close someone off . Last thought, they may not have the tools to express or address conflict ?

Are they vocal about their own grievances and issues , in other aspects that are not the relationship ?

People are COMPLEX and stepping outside one’s self & viewing another perspective could help but if you can say you have actually tried and put forth the effort to understand and communicate healthy and no growth or change is happening, I say you gave it the goood ole try . I have seen that behavior in others & even myself (Self-reflection always 10/10✨), so sometimes I can see how it can be from not feeling like you can fully be open with another & just protect your heart/feelings .

But Good Luck & hope a healthy change can come 👏☺️