In this sentence, the word SLOWLY is describing how he walked home.
This means that it has to be an adjective.
This simple the answer should be “since” because it’s proper grammar
Maniac<span> Magee is a novel written by American author Jerry Spinelli and published in 1990. ... He has astonishing athletic abilities, runs everywhere he goes, </span>can<span> untie any knot, is allergic to ... </span>Piper<span> and Russell </span>McNab<span> are John </span>McNab's<span> younger brothers who play hookey, steal, and constantly try to run away from home.</span>
