I still believe that Saku ultimately just wants Susa's dick. All this being cucked by Susa and then turning around and fucking his girlfriend to make Susa feel the NTR too ... sounds like petty nonsense that jealous people do to get the attention of the one they really want.
Also to everyone who thinks this is NTR... there is no such thing as consensual NTR or Mutual NTR. NTR involves being helpless while the one you love gets fucked right in front of face with the option of you being forced to clean up afterwards. You have no choice and you do not get a concession pussy to fuck either.