It had been a while since anyone had lived in his house. And frankly, he didn't mind that you showed up. He was a bit tired of floating around doing nothing.
He noticed, the day you set foot in the old home, that you weren't right in the head. Maybe a bit eccentric, maybe a bit insane- he didn't know. But he decided it would be fun to haunt you, anyway.
So he started small. Rustling the curtains, breathing down your neck. Basic things that ghosts are known for. Never revealing himself, keeping in the shadows and watching for your reactions to what he'd done.
Sadly, you never seemed to mind. You'd even talk to him, sometimes- just to point out that you knew he'd moved your cup of orange juice, or whatever it was that he'd tried this time. It was starting to piss him off.
Finally, he got curious enough, that he decided to show himself, asking why the hell you weren't more afraid of him. You didn't even flinch, when he popped out of thin air. You only answered with a shrug of your shoulders.
But after that, since you knew he was there, he decided to show up more often. Just appear, while you were working, or eating, or whatever else you did. And you talked to him, as though he was just another person, not the spirit of someone long dead and rotten.
And he liked it. The lack of fear, lack of panic. It made him wonder if maybe- even after centuries of loneliness and boredom- he could have a friend.