Change your locks. Send him the bill. And if he argues, press a trespassing suit against him. This is incredibly far out of bounds UNLESS it's something like "I borrowed the key from your Mom so I could sneak these flowers onto your table for our anniversary, as a surprise". Sneaking creepiness? Yeah. He's buying you a whole new set of locks at the hardware store, and he's NOT getting a key...nor is he getting to borrow your keys, ever again. I bet he "borrowed" your car...to take the keys straight to a locksmith and get a copy.

If you guys break up, he'll never be gone.

It's time to call the ghost busters

I'd like to think maybe he was trying to plan some romantic or b-day surprise, but copying a key without permission is way out of line no matter what is going on. If the relationship is not serious enough for someone to have a key of their own, (or to borrow a key from- or be let in by- a key-holding friend or relative), then such a surprise is simply inappropriate. If still up for it, plan it at one's own place. No need to go to creepy-stalker status.

time to talk with him

That's concerning.

creepy!

This deserves an update follow up for sure

Time to change the locks......... like right now!!!!!!!

that guy must be drinking too much vodka.