Most of what I’m seeing here sounds too confrontational or passive aggressive to me. What I would do personally is wait until he asks you if everything is okay again and then say something like this:
“Yeah, all good here. So you know, I’m not quiet because something is wrong in my life or between us, I’m just very introverted and my natural state of being is not to open up”
Most people tend to assume other people’s internal state is works similarly to their own, unless it’s an aspect where they know they are far removed from the norm, so for an extrovert, they equate you being quiet to what would cause them to be quiet. Without telling him the reason you act differently, he will continue to assume this.
By wording it as an FYI, you give the opportunity for him to understand the difference and change his behavior without telling him he has been doing something wrong, because best as he knows he hasn’t been, and so you hopefully prevent him from getting defensive.
If he continues, then maybe you can go to a more confrontational approach. That’s how I would handle, at least.
I am also a woman and I’m guessing you are not from your username, so ymmv with communication like this.
I hope this comes off the way I want it to: remember this is about you. You sound like the sort of person who is always putting others first, which is an admirable quality, but this is all about you—everyone who cares about you will immediately recognize that.
Don’t waste your energy trying to protect anyone else’s feelings. The best thing you can do for your loved ones is tell them as soon as you can (even if that means just being super blunt about it) and focusing your energy on your plan to maximize health/minimize pain, which they can all help you with.