I'm considering apping Allie here, who is an OC, and I'm pretty flexible about her background. If you're looking for someone who could possibly serve as a bestie, I have some ideas we can play with. How old are you planning on making him, roundabout? Allie's age is flexible. Also she can see/detect/attract ghosts and spirits, it's a lame candle ability.

* Allie gets kicked out of her foster family house around 15 and just kind of hangs around as a thieving delinquent for a while. Jack could be the one that turns her toward less harmful delinquency and show her the meaning of fun, she can show him how to hotwire a car handle being a regular person in the city.
* They both have a tough time handling basic necessities so they pal around together, steal food, find a decent place to hang out and sleep (he'd be especially handy in hotter states like Texas as he'd be a walking air conditioner and Allie hates anything hotter than 80F).
* If you do decide to go the route of 'normal people can't see him' then Allie could have known him since she was a kid, and got frustrated when no one believed her, so she gave up and grew up just knowing him for some period of time -- maybe he was always there, maybe she blamed him for a foster family rejecting her for lying and told him to scram, etc.

Just a few ideas, you don't have to go for any of them. But it'd definitely be fun to start out with some CR in the wings!