This has been going on for three months.
The first time I met him, he was weirdly cold with me. Barely spoke, kept staring whenever my sister and I joked around.
Finally she asked what his problem was.
Turns out he saw an old family photo, didn’t realize I was her brother, and has believed this entire time that I’m some ex-boyfriend who is still suspiciously close to the family.
Nobody knows how to recover from this.