In the third season, Spider-Man officially joins the Avengers, but after a fight with Loki, Doctor Octopus and a group of Norse creatures bonded with the Venom symbiote, he chooses to resign and remain with S.H.I.E.L.D.
Later on, Madame Web comes to the conclusion that the destruction of the Siege Perilous during the fight with Doctor Octopus and alternate Green Goblin has shattered the dimensional barriers between numerous worlds.