I think over Neil’s sophomore year at PSU he slowly starts to reveal his real, unfiltered personality, and each of the Foxes have their own realization of why him and Andrew are actually perfect for each other.
If they thought Andrew was crazy, just fucking wait until they see Neil truly angry, until they hear about some of the things he’s had to do, about his own twisted morals, until he stops faking emotions to fit in and instead allowing himself to remain blunt and seemingly emotionless half the time. He’s not at all the boy they thought he was, but they love him all the same.
This also causes them to rethink their opinion of Andrew - they saw the rough parts of him first, whereas Neil’s came out later. Maybe there’s more to Andrew after all, especially as he starts allowing the occasional emotion to slip out.

