So this is going in the direction of MC getting gaslit into crossdressing more and more. Man I had hoped it wouldn't go this way. This is now per definition a toxic relationship.
He did take a real bad hit to the head as a child when his sister shoved him off the jungle gym. Him having brain damage as a result would not be remotely surprising.
First off: There is no such thing as Reverse NTR. NTR is NTR regardless if it's man or a women getting stolen from.
Secondly: This is more BSS than NTR. BSS = Boku ga Saki Suki = "I Loved him/her first."
The thing with social connections is if you have reset them once, doing it again is easy. Given that Akira has transferred around a lot he is able to cut ties very easily.