
Continuity mistake: In the Thanksgiving dinner scene, watch Mary Jane's arms after Norman asks Peter to repeat how he got hurt. When she is shown close up, her arms are folded. In the long shot, her hands are in her lap. They jump back and forth between the two positions. (01:24:50)
Answer: Remember that Green Goblin (Norman Osborne) just found out that Peter Parker is Spider-Man. Aunt May's comment about everyone knows he loves Mary-Jane concerns him because he now realizes that Green Goblin might find/kidnap Mary-Jane just to lure Spider-Man into a fight. This is the basis for the whole reason he can't be with her, as he would be potentially putting her in harm's way all the time if they got together.
Jazetopher