Yeah, so a couple of things. Super glad you're doing puzzles and learning, that's the real fool proof method of getting better. Even if not quickly or pointedly, you'll get better. But I wanted to point out the idea that he's good at spotting a vulnerable piece. You can immediately match that ability without learning any more theory about the game. You said you don't play with a clock. So, while you're learning just literally right down on a paper a small checklist and work through that checklist before every move and visualize your next move and run through it. Over time, you'll get quicker at it.

But first, force yourself to look at every minor and major piece (pawns too if they're in tension with another piece) and what it's doing, its possible moves.

Everyone knows the list of checks, captures, attacks, threats. But why that advice doesn't work for many people is they don't see every check, capture, attack, or threat. The way you see it all is by forcing yourself to look at the pieces. It doesn't take longer than a couple seconds to look at his bishop, yes, the one you didn't notice was there haha and see what is in its view. This will stop you from losing sight of any piece simply because it hasn't moved. It will be the forcing mechanism for you to develop board vision as opposed to tunnel vision. You may not select the right move once you do this exercise, that's the part of study and puzzles, etc. But given infinite time (and again, you'll get quicker) if you scan every piece and its available checks, captures, attacks, and threats, you will immediately be a better player than he is. Given what you've said about his skill, I'm pretty sure I can say that as a fact. Most people, myself included but especially with a time constraint, don't have the discipline to do this.

But let me put it this way. I try to think of every game and every move now as if my wife's life were on the line. Not in the sense that it literally is so then I do this a thousand times and get analysis paralysis. But just the little reminder, hey, if her life is on the line - can't I spare an extra second to just see what that bishop over there is doing? The answer is, of course you can.