I don't believe anyone said you're guaranteed to be cheated on (or cheat on) in every relationship you're in, which is what you'd imply with "during the course of their relationship". The discussion --at least on my part-- was in context of people's entire lives, typically meaning multiple relationships, and the cheating occurring during one (or more) of those relationships. Which, you'd have to admit, is highly probable from simple statistical point of view. (the likeliness of cheating increases with age, particularly from 40-50 onwards)If you actually believe that one or the other will inevitable cheat during the course of their relationship, that’s fine but it’s factually incorrect that this is always the case, and to assume so is frankly imo a sad state of paranoia when lots of people have gone through relationships without cheating.
In any case yes, there isn't much point in continuing this. If you manage to spend next 3-4 decades of your life without ever cheating on your partner (and without getting cheated on) congratulations on beating the odds. If not, i don't really expect you to come back here and admit that hey, maybe there was something in that claim after all.