True, to some extent. But also, he should know and see it coming, and people in his entourage should also see it and be briefed/watched by services.

It's a cat and mouse game. Obviously, the adversary will in turn do everything in their power to make it look natural and get past that kind of defensiveness.

Perhaps as far as to say, the only suspicious thing about the perfect agent would be the lack of anything to be suspicious of.

I mean he should just not have an affair, independent of whether the other person is a spy or not.