I guess if I read you correctly there should be no physical contact at all between unmarried persons? Because obviously intercourse is wrong before marriage and even a goodnight kiss can cause arousal.
I am not being flippant, I am trying to understand. I did not go to Catholic school so I guess I am deprived!
There is a simple rule of thumb for unmarried people. If the act they are contemplating cannot be done in front of their parents or the general public, they should not do it.
Normal unmarried people can kiss each other goodnight, or give an embrace, provided it is not done for the sake of pleasure. St. Thomas Aquinas notes:
"A sin is called mortal by what sort of action it is in itself and by what it is caused by. On the first count, kisses, embraces, and caresses signify no mortal sin. They can be done without libidnousness according to the custom of the country or from some fair need or reasonable causes ... Now we have noticed already that consent to the pleasure, not merely to the act, of a mortal sin is itself a mortal sin. And therefore since fornication is itself a mortal sin - and other acts of lechery much more so - to consent to its pleasure is to be gravely wrong. Consequently when kisses and embraces and so forth are for the sake of this pleasure they are mortal sins. Then only are they called libidinous, and to be treated as mortal sins. (Summa, Pt. II-II, Q. 154, Art. 4)
As to other expressions of affection between unmarried people, the following is a common opinion of sound moralists:
In the relationship between a boyfriend and a girlfriend, assuming there is no lustful intention, an expression of affection, which is acceptable but not necessary, which produced an incomplete disorder [sexual arousal], would be a venial sin, if the disorder is positively rejected, but it would be a mortal sin to continue this same action if it involved the proximate danger that the disorder would become complete. (A. Lanza, P. Palazzini, Principles of Moral Theology)