Early in the first episode, when they were alone in the upstairs hallway of Paul's house where nobody else could hear them, their dialog was supposed to tell us that (among other things) they had not seen each other in decades and were not friends.I think Will and Paul just played it as they were acquaintances rather than friends, so Will could remain on the case, since he had the best odds of getting it solved.
Seems kinda creepy that someone you didn't like and haven't seen in 25 years can find out where you live. We only know what we've heard in the dialog — Paul struggling to remember Trent's nickname and what it meant, Paul not knowing their group home manager had died, Paul remarking he's surprised Trent and Angie are still together, and so on — none of which explains how he knew, at 3 in the morning, where Trent lived. Maybe that explanation was edited out.Just because they aren't friends doesn't mean that Paul doesn't know where Will lives, though. They knew each other, so it wasn't like he knew where some random GBI agent he'd never met, lived.