So the NTR is not avoidable then. That is unfortunate.
It is avoidable, just do the following :
Do not run out of AP (and unless you use a warp gate, returning to town will cost 1 AP, so remember that), additionally, keep 6 padlocks in inventory as a just in case (I.E, you get really bad RNG and return to town with 0 or minus AP), padlocks will prevent the Innkeeper from getting into Monica's room (borked in the official version, it crashes the game, currently waiting on a fix/update)
Pay the guild (very easy to do, grab the quests from the guild, and do enemy camps whenever possible, as they are a guaranteed chest afterwards, sell loot to store or night merchant at the guild)
Do not lose boss fights.
The priest will pressure Monica into "paying" for MC's treatment if he is KO'd on encounter
honestly, people acting like the NTR aspect is gonna happen regardless of how they play, it is 100% avoidable.