St. Francis de Sales: seculars must "form holy and sacred friendships"

[Geremia]

Particular friendships are necessary for seculars (but not for monastics). St. Francis de Sales wrote in ch. 19 of Introduction to the Devout Life:

For since in a well-regulated monastery the common aim of all tends to true devotion, there is no need to form particular friendships there, for fear lest, making a particular aim of that which is the common aim, they pass from particular friendships to partialities; but as for those who live in the world, and who embrace true virtue, it is necessary for them to form holy and sacred friendships with one another; for by this means they encourage one another, help one another, and lead one another on to good.

[Geremia]

Ecclesiasticus 6:7: "If thou wouldst get a friend, try him before thou takest him, and do not credit him easily."

St. Alphonsus di Liguori, The True Spouse of Jesus Christ, ch. 10 "Detachment from Relatives and Other People" (ref:836.1), §2 ("Detachment from seculars") lists (ref:836.37-42) St. Bonaventure's criteria (De Profectu Rel. l. 2, c. 27):

• It is not pure when it leads to long and useless discourses; and when conversations are very long they are always useless.
• When each delights in looking at each other and in praising each other.
• When either excuses the other's defects.
• When they manifest certain little jealousies.
• When either feels unhappy at being separated from the other.

Also, a good litmus test "of the carnality of spiritual affection" is "if the passion of love (passio amoris) precedes the affection of the will (dilectionem voluntatis)" (De veritate q. 26 a. 7 "Does a passion accompanying a meritorious act detract from its merit?" ad 7).

[Kephapaulos]

I imagine the Angelic Doctor and Seraphic Doctor fulfilled the opposite of the above criteria in their mutual friendship, each having entered the beatific vision a few months apart.