You can pursue whomever you feel like pursuing romantically, may that be a monogamous relationship with only one character or have several relationships with several characters, if you mean to say if you just want to have sexual encounters with only one character that gets hard seeing as a lot of the game runs around sex, it doesn't force you into anything tho.
All the CGs in the game come from seeing other characters having sex since the MC is a blank then all sex scenes that involve them don't get CGs and never will, tho the NOC sprites(when they have it already) will change according to the scene