Rarely alone, never two, always three.
It was a saying commonly heard, along with others, in Catholic schools and not just Jesuit ones. I heard it in a Jesuit elementary school but also later in a college run by Dominicans and later still in a place run by Salesians. They all said it. It was said in French (rarement seul, jamais deux, toujours trois), not Latin, and the same phrase was apparently used in parts of French Canada according to the retrospective study below entitled "Between honest friendship and Socratic love", spanning 1870-1960. I cannot find an English translation but here are some pertinent lines that I will translate for you : "Les dortoirs font ainsi l’objet d’un contrôle assidu ; l’habillage, le déshabillage et la toilette sont réglés par un rituel strict visant à préserver la vertu et la pudeur. Les promenades et les jeux s’accomplissent dans le respect d’une maxime : « rarement seul, jamais deux, toujours trois[61] ». Le personnel surveille le courrier et fouille les pupitres....
The dormitories are thus subject to an assiduous search; dressing and undressing and washing are ruled by a strict ritual designed to preserve virtue and decency. The walks and games are performed in compliance with a maxim: "Rarely alone, never two, always three." The staff monitors mail and search desks......."
In short, this adagium or saying is indeed internationally used, in different languages and different settings but mostly in Catholic schools, colleges and seminaries. There are many of them, along with prescribed practices such as putting a crucifix on top of your bed (not on the wall but on the bed itself) after you've made it up, not eating certain foods, the "judicious use of eyelids" and many, many more.
http://www.erudit.org/revue/haf/2004/v57/n4/009639ar.html
