Sounds very similar to what I had. Back in the 8th grade or so, I dislocated my left kneecap in school while picking up a piece of paper infront of the secretary’s office.
When she opened the door in response to the screaming and saw my kneecap was off to the side, she looked like she was about to vomit or faint
It slid to the side randomly during a benign activity because it was apparently kinda loose in the first place. The dislocation then aggravated that issue to the point of requiring kneecap stabilization surgery.
In other words, screwing the kneecap in place with titanium screws.
I’m guessing that’s the same surgery your fiance required?
That surgery is absurdly painful