Peter = The weight of being Spider-Man continues to burden him but he never entertains quitting because it is his destiny, his curse despite the toll it's taking. He thinks more and more about the people he's lost as Spidey (Ben, Norman, Otto, Harry, etc.) with the main villain of 4 (Vulture) exploiting this after figuring out his identity while also sending Black Cat to seduce him to no avail after she has a change of heart; After being buried alive by Kraven in 5, Peter hallucinates/dreams of those he has lost as he goes back and forth in his head about staying in his grave to die before fighting his way out to save Curt Connors' life even at the cost of his own
MJ = Amicably splits from Peter between 3 and 4, while remaining friends, as she goes to Hollywood to become a moderately successful actress; Peter reaches a low point at the end of 4, spurring MJ to reunite with him at a funeral and they get married soon thereafter; The series ends at 5, where she tells Peter she's pregnant
JJJ = Peter quits the Bugle for a better job, leading to a hilarious running gag in 4 where Jonah tries to win Parker back but to no avail; Despite this, the Bugle staff is invited to Peter and MJ's wedding; Inadvertently lures Kraven the Hunter to NYC with a bounty in 5 after several Lizard sightings go unanswered by Spider-Man, who JJJ finally realizes has been Peter all along and prints a positive cover story about at the end
May = Is revealed to have cancer in 4 and deteriorates throughout despite her caretaker, Felicia; Passes away at the end after revealing she knew Peter was Spider-Man all along but her death brings Peter and MJ back together; Appears as a hallucination to Peter in 5, encouraging him to press on as Spidey alongside Uncle Ben and Doc Ock while the memories of Eddie Brock and the Osbornes serve as deterrents
Oscorp = Goes out of business in-between 3 and 4 but has it's military technology recycled by criminals known as The Sinister Six (Adrian Toomes, Felicia Hardy, Quentin Beck, Herman Schultz, Aleksei Sytsevich and Wilbur Day), supervillains that are eventually defeated consecutively by Spider-Man
Ditkovich = Finally gets his rent as Peter's new job in 4 pays better and is invited to the wedding in 4; MJ's job as an actress allows her and Peter to move into a house together at the start of 5, allowing for an emotional but hilarious goodbye at the apartment
Sandman = Is revealed to have turned himself in between 3 and 4, landing in Ravencroft; Rejects Vulture's offer to take Black Cat's place in The Sinister Six and break out as he teaches the villains during a game of power that with great power comes great responsibility by telling his story of facing Spider-Man
Gwen = Grows to become friends with MJ and ends up dating Flash around the time of her father's funeral in 5
Connors = Peter goes to work for him as his assistant in 4; Is seen working in his lab and is revealed to have turned into The Lizard at the end; As the main villain of 5, his wife and son looking for him puts extra pressure on Parker to actually save him rather than let him die like previous villains; Gives Captain Stacy a fatal heart attack during a chase into the sewers; Following this, Kraven takes out Spidey and tries to hunt the monster down with lethal intent; Peter uses an anecdote to turn Connors back to his human form and does not send him to Ravencroft (Vulture, Mysterio, Rhino, Shocker, Stilt-Man and Sandman are already there) with Kraven like expected, allowing him to be the family man he always wanted to be