@vanejournalist that is reactive, because in that case you are still waiting for somebody else to do something or not, yet you just want to catch them in the act.
Assuming responsibility for your relationship means that you treat your partner in a way that makes him or her not want to be unfaithful, and if it does happen to have a close look at what you yourself did or didn't to prevent that from happening.
Simply spying on someone isn't going to change their feelings and thoughts, putting in effort in your relationship might.
Then again, some people are just dicks and no matter how good they have it at home they will always look for something on the side.
Very well, now if I understand your point, thank you very much for clarifying.