Stiles quits the FBI program upon seeing Derek in the FBI watchlist files and decides to find him and help him hide. It takes a couple months, but when Stiles finally sees Derek boarding a bus, he feels a sort of peace fall on him and he realizes that what he did was the best decision. This is where he should be, this is his calling. To be with Derek and to live in the supernatural world.
He and Derek spend a long night talking and arguing in a hotel room and in the early hours of the morning, they finally settle on hiding from the cops together. Stiles wouldn’t have had it any other way, he had to fight long and hard on his way to Derek and he wasn’t going to back down easily. Derek knows Stiles had realized his feelings and he knows that Stiles will never leave or let Derek leave; not when Stiles proved that he can fight for himself and fight for Derek if need be.