Dude for the the last time it will not make his choice cheap or wrong or whatever the hell you think it is. It will make it realistic.
He would feel betrayed by luna because after all these years she hasn't been thinking about him at all.
And another thing. He is a cuck. This might not be netorare. But there is a lot of cucking going on. Think about it. Every other guy has a one night stand easily with luna and naoto gets put in the brotherzone? That is just pathetic but the fact that naoto accepts it makes him a cuck.
It doesn't matter what choice Naoto makes, if Atsushi follows through with the matching app, the series is heading to an abrupt end and nothing matters because it's going to be rushed in a way that closes out the narrative as quickly as possible.