Well, here's what I think will happen in the Second season finale (note I haven't seen the episode yet so all of this is pure speculation):
*After breaking up with Liz, Peter declares his love for Gwen when he tries to warn her about Harry (because he believes [blackout]he's become the Green Goblin again[/blackout] and she returns it, but this happens right when Harry walks in, and Harry, hurt and angry, storms off.
*The Green Goblin takes Gwen hostage, which results in the arrival of both Spider-Man and Captain Stacy. Spidey manages to save Gwen, but during the battle with the Green Goblin, Captain Stacy gets injured and falls into a coma. Enraged, Spidey beats the Green Goblin to a pulp and the Goblin is unmasked as...The Chameleon.
*Afterwards, Spidey goes to Norman Osborn to get answers and while there, Osborn manages to ambush Spidey and unmasks him. He reveals that he was the Green Goblin all along. After explaining to Peter what he did as the Goblin and how Harry and the Chameleon were involved, he lets Peter go, knowing full well that Peter can't do anything to stop him because, since the world thinks the Chameleon was the Green Goblin, and Norman could reveal Peter's secret the moment he tries to expose him. Norman will just sit back and watch as Peter gets hunted down for his culpability for what happened to Captain Stacy and tells Peter he can now go after him or his loved ones any time he feels like it, so now Peter will forever have to look over his shoulder.
*When Peter goes to see Captain Stacy in the hospital and with Gwen, she tells him that it's a bad time for them to be together, and she blames Spidey for what happened to her father, thus Peter feels that a relationship with Gwen now would be impossible. Feeling he's lost Gwen and now a fugative, Spidey decides to quit and, in a "Spider-Man No More" homage, throws his costume away when he gets home. However, the costume is then found by...Mary Jane.
Guess we'll find out soon enough whether or not any of my predictions are right.