I think it would be smart to keep the MC on his toes regarding potential NTR. The MC is young and inexperienced and playing with his jealousy would also keep the player on their toes as well.
You could potentially keep the player in the dark, for example, have times where we see or hear some shady things that Vi has been doing but without any confirmation. The MC/player could be teased by Vi regarding the unknown situations.
I also want to see the MC teased about:
- larger cocks (MC's is a good size)
- his performance in bed (I don't think MC should be bad, just inexperienced and that other guys have more knowledge and may be better)
- other girls (teasing MC about finding other girls attractive)
- incest (teasing MC about finding his step sisters / mom hot and wanting to fuck them)
- his friends (teasing him about his friends being good looking, wanting to fuck them)
- threesomes / group sex (both mfm / mff etc.)
- If the story goes to a new school year, fucking the teachers
- Streaming / camming / Onlyfans content (teasing MC about the comments and requests)
- Beaches and swimsuits / exhibitionism
- Cheating
- Other guys being more attracive
I'd also like to see some fights between the MC and Vi for some makeup sex and areas that are unknown (did she fuck x while we were on break etc)
With rising jealousy, fights between MC and other guys. Maybe the girls fight as well.
EDIT: Just to be clear, obviously these suggestions would start slow and and ramp up with time.