The only way i can think this could happen is if..IF he/she was using your wifi and then got control of your computer. That would mean someone close, not much more than next door.
This is why I change my passwords periodically. And don't make it easy for them to decode. I use 5 random 5 letter words and uppercase one letter per word in random positions.
Xxxxx xXxxx xxXxx xxxXx xxxxX (not how I do it but you get it)