TIFU by stabbing my fiancé

So last night around 1am my fiancé and I are woken up to a bang coming from what sounded like our bathroom. It sounded like someone dropped the toilet seat or something. No one else lives in the house with us so my mind immediately flashes to intruder.

I asked him if he heard the noise and he says yes, he'll go check on it when he gets up for work in a few hours. I said someone needs to go check now, because an intruder isn't going to wait a few hours to end us. He insisted he'd check later so I decided to go check, I wouldn't be able to go back to sleep is someone didn't.

Our house is small, you can pretty much see the whole thing from the center. I glance around, both doors are locked and there's no one in the kitchen, livingroom, or office. Strange thing is that the bathroom door is closed. I always leave this door open overnight because we have a weirdly placed air vent in the bathroom that turns it into an icebox or oven if you leave the door closed.

At this point I'm spooked, especially because I have to open the bathroom door to check. I go into the kitchen, grab a knife, and prepare to open the door. I open it, see there is no one inside, and realize that the noise was caused by our shower caddy falling.

As I am making these realizations, there is a voice behind me. I scream, turn around and jab the knife forward. Turns out my fiancé decided to get up anyway and find out if I was okay. I definitely sliced his arm. Luckily it was extremely superficial and he was standing away enough that no vital organs are in range. Who sneaks up on someone in the middle of the night? Anyway, we definitely lost the rest of the night to the adrenaline of me getting spooked and him getting stabbed.

TL;DR My fiancé snuck up on me in the middle of the night while I was checking for an intruder and I got spooked and stabbed him in the arm.