Complex sentence: While at Drevin's home, Alex starts to befriend Paul, but decides to leave him and his father once they arrive in New York in route to Flamingo Bay, the reason being that Nikolei Drevin nearly killed him in a go-kart race.
Split into simpler sentences: While at Drevin's home, Alex starts to befriend Paul, but decides to leave him and his father once they arrive in New York in route to Flamingo Bay. Alex leaves because Nikolei Drevin nearly killed him in a go-kart race.