As Natasha approaches the subway station on Fifty-Second Street, she watches a couple, both with bright blue Mohawks, arguing. The woman looks enraged; the man looks exasperated. Natasha wonders if this will be the last fight. She thinks that they were once in love and might still be, even though it doesn't look like it now.
Natasha's interpretation of the fighting couple (namely, that she's not sure if they're still in love) shows that she understands now that reason isn't always going to be an effective tool for understanding something emotional, particularly when it doesn't include her.