Okok so I know this is completely unrealistic, but follow along for a second, Jean instinctively gave Cat a forehead kiss right? Just hear me out, Neil. Neil and Jean having spent like a week together and finally having to go their separate ways again, giving each other an awkward side hug, but Jeans a little more mentally healed, affection is becoming second nature, so he doesn't even think about it when he kisses the top of Neils head, who just stands there, completely flabbergasted with a "wtf" pinch in his eyebrows and a few processing blinks. Jean goes to let go of him, but Neil looks up, still holding them together, with a devilish smirk. "Did you just kiss me?"
"You just kissed me." Neil gets in front of him with a mocking smile.
"It was a mistake. Go home."
"No, no, no.-" Jean tries to step around him, muttering swears in French. Neil crosses his arms, still standing his ground. "What if I want another goodbye kiss?" Neil quirks an eyebrow with arms crossed over his chest.
"Most definitely not, but Ill leave." Jean lets out a frustrated huff, grabs the sides of Neils face and pulls him forward in a harsh tug, kissing his forehead with an aggressive bump. Neil beams up at him, gives a nod, then turns to leave. Jean doesnt watch him walk away, pissed at himself.
I can imagine Andrew finding out about it and not at all knowing how to feel, not necessarily jealous because Neil doesnt swing, but possessive in the sense that Neil is his to kiss. Or Jeremy watching this whole scene from a few feet away just thinking "how do I get goodbye kiss privileges?"
Neil makes it become a thing everytime they are together, he just won't fucking leave until Jean kisses the top of his head, eventually it just turns into Neil basically headbutting Jean's chest and Jean instinctively bends to bury his face in Neils hair. Neil notices Jeremys sad/jealous expression at one point and tells Jean "looks like someone else is waiting for a goodbye." Motioning at Jeremy, when Jean turns to face him, Jeremy looks away with a pout. So of course Jean walks over and kisses the top of his head as he walks by to get in the car. Jeremy faces goes bright red as he locks eyes with neil who scoffs then winks at him before leaving.
Andrew witnesses it once, at first he is immediately defensive because Jean didnt ask, but the proud look on Neils face is enough for him to back down, to not hurt Jean because clearly Neil enjoys the attention, however it doesnt stop Andrew from leaving hickeys on Neil basically head to toe the second they are alone.