Well done, @Wilhelmine!!
You see, I get he might have picked up by mistake, but .............
Think it through. There must have been that moment, when he got home, that he let himself in. And not with your keys. With his. So if he'd got yours by mistake, he would have found that out when he tried to use them on his door.
Unless he's weirdly forgetful snd out your keys in his pocket then used his own as they were to hand. But still, that's unlikely.
I think he knew when he got home, at the latest.
And when you asked him, if his look the same, how did he know he'd got yours? Because he'd either found out the mistake the night before, or taken them on purpose.
He can't have thought you wouldn't miss them, though.
It's weird he didn't call snd tell you when he found out.
All strange. Great about your new locks!
He's already jealous if your exes. Omg.
Retreat. Withdraw. Be clear.
Hope you're ok. Sleep well! : )