Jen and Johanna have very good advice. TNRing is probably the best way to go. Build him a little insulated shelter and make sure he's being fed. I am now feeding the white and black cat that kept getting caught in the trap while trying to get Eli back. This cat is definitely feral. So I made him a shelter and feeding station in the backyard with my landlord's permission (he doesn't care). I plan on trapping this cat again in a couple of weeks and having him fixed and putting him back out. That's where he seems to want to be. As long as he's cared for, that's what I'd do.