Yes, every teacher will figure it out, but teachers shouldn't be looking to figure it out, they shouldn't be looking for it, if you know what I mean. They have other things to worry about other than student relationships.
And yes, I do want exact dates, or the punishment would be sooner/later for each person. But who is to decide these dates? And who is to say that dating one month is different than dating one month and a day?
I'm arguing that 1). There is no way to really define "steady dating" without some arbitrary numbers, and 2). Because there is no way to define steady dating without being arbitrary, and because this is an invasion of student's privacy, there should be no consequence on "steady dating"