How I communicate?

I don't know how to express to him that some actions hurt. He's not a bad person, but some actions make me insecure. (Sometimes I feel like I'm in second place, or sometimes he oversteps boundaries, like how he dedicates his time to the relationship. For example, he assumes that because I'm busy, he won't tell me what's going on or why he's sad, and he decides for me and doesn't reach out. And that sometimes makes me feel guilty for not being available or free all the time for my partner.) And that sometimes makes me feel excluded from his life.

But the point here is, I don't know how to do it in a way that doesn't make him feel guilty or think that he's a bad partner when we start a conversation like that, about actions that hurt one or the other. I promised him not to keep my feelings to myself when something hurt me because, whether I like it or not, it's very hard for me to express myself, and I tend to withdraw and have a less loving attitude. And the fact that this has recently caused us to avoid our conversations, and that they have escalated into arguments where we ignore each other or withhold affection, scares me that he'll pull away. And now I'm afraid to open my heart to him, only to feel these kinds of insecurities and for it to hurt a lot. Some actions are important to one person, but not so important to the other, you know? It's true that there are very different acts of love in each person, and I would like him to see my perspective and me to see his, but I don't know how to start a conversation like that so that we don't end up arguing about who's right and it turns into an ugly argument.