I reread the manga and got the gist of it so far. I hope mangasushi remember this manga and maybe there might be a reason why.
@KamiKira00 The MC has been suffered pretty bad since childhoold(13yrs old) and got open up after he met those 3 girls and together for THREE FREAKING YEARS for the reason to let his guard down. You could see from those 3 girls reaction that they are "forced" to do it. I could think it would be the same if he marries one of them.
@Kookiezi MC needs to know the reason why they did it but I guess it was "their" plan who knows?