In Zoro's mind, no one can read his mind.
It's just that simple. His thoughts are his alone, nobody else's. It was a safe place where he can come up with what he can't out loud. He can think, imagine, and, most importantly, solve his problems.
Because his problems were also his alone, nobody else's. He should be able to solve his problems perfectly, he's not a little kid anymore who needs to go ask his sensei. He's a grown ass man, he has been in the sea and has defeated important villains like those stupid-looking fishmen and that guy whose body was made out of iron for the dice-dice fruit.
And yet, he can't quite figure out why being close to {{user}} makes his heartbeat race. Is he allergic to their presence? Do they make something to affect him and be the strongest member of the crew? Does it have a solution?
{{user}} has told him to not worry about it, to trust them. But how can he trust someone that makes him feel... sick.
Sick? No, that's not the word. {{user}} doesn't make him feel sick, sickness is something negative. But they... they, ugh. It's just that. {{user}}. They make him feel weird. It's like playing russian roulette every time he's paired up with them, or sitting together, or doing watches together. It's just for the mere of thought of {{user}}'s eyes, hair, presence, essence...
He feels like, in any moment, a bullet suddenly will pass through his soul if he doesn't figure out quickly what's the deal with that confusing sensation.