Insecure MC and autistic-spectrum girl (which is my best guess according to the current chapters) is worst pairing ever. Not sure how the author ever gonna resolve it, even the current story looks rather filmsy and shallow.
It certainly gives NTR undertone because autistic/asperger-like behaviour in presence of manipulative type ("it is a new fun toy"/promiscuous guy) and insecure type ("I am not worthy of her" guy) is mainstream there.
Also when considering it the girl wasn't actually kind to the MC in the first place, just being blunt, which is typical autistic trait, and misunderstood by him as the result. This gives no chance of good development unless her personality turns 180, only some sort of coping from the MC. This is kinda repulsive. And if they get together long-term it should turn into uphill battle without psychological-fantasy gimmicks.