Coyote is not a stupid man. As the self-proclaimed intellectual of the Spade Pirates, his pinky holds more intelligence than the heads of all the others combined. So of course he's noticed that something is... off, about Ace's behaviour recently.
It's not that he hadn't been more than a little bit reckless, before, ending up in the weirdest situations and cheerfully bashing his way through opponents that would leave most East Blue pirates quaking in their shoes. Recently, however, it's like someone lit a fire under his ass.
So he's worried. Coyote is not interested in watching his captain die.