Seems that some super vanilla guys are not okay with a option to cheat on girlfriend. But, I'll assure you that isn't a deal breaker for tons of majority players when compare to the vice-versa i.e. Girlfrnd cheating on MC (which won't be in this game as stated by dev himself). This game thread would have seen another war thread if this game contains that NTR elements. 
And who knows, may be the girl friend will accept the way MC is, may give free pass to him while she keeps faithful & may be become even a cuckquean too.