What are some ways I can navigate challenging discussions with my boyfriend?

I'm a 27-year-old woman in a relationship with my boyfriend, who's 32. I’d like to discuss some feelings I've been having lately. While he’s been spending time with his family over the past few days, I’ve had a chance to reflect on our relationship and consider where I want it to go. Lately, I’ve noticed that he seems to have become a bit too comfortable and hasn’t been putting in the same effort that he did when we first started dating. I’m not expecting him to change because I know that it has to come from within, but I really want him to understand that I’m not feeling the level of love that I need. I believe in our relationship, but I can’t work on it alone. He knows I'm afraid of losing him, but I don’t think he realizes how close that fear is to becoming a reality. One challenge I face is that when we talk, especially if he gets upset, I tend to shut down. I struggle with PTSD from my childhood, which causes my mind to go blank, leaving me unsure of how to continue the conversation or find a resolution. I often consider writing down my feelings, but that approach feels insincere to me; I’d rather not read from a script, even though that’s typically what I would do in such situations. I’m looking for advice on how to have these conversations without freezing up. If anyone has suggestions for gently expressing my feelings without making it sound like I’m attacking him, I would greatly appreciate it.