From Summa Theologiae, IIa-IIae, question 23, article 1:
Objection 1. It would seem that charity is not friendship. For nothing is so appropriate to friendship as to dwell with one’s friend, according to the Philosopher (Ethic. viii, 5). Now charity is of man towards God and the angels, “whose dwelling [Douay: ‘conversation’] is not with men” (Daniel 2:11). Therefore charity is not friendship.
Objection 2. Further, there is no friendship without return of love (Ethic. viii, 2). But charity extends even to one’s enemies, according to Matthew 5:44: “Love your enemies.” Therefore charity is not friendship.
Objection 3. Further, according to the Philosopher (Ethic. viii, 3) there are three kinds of friendship, directed respectively towards the delightful, the useful, or the virtuous. Now charity is not the friendship for the useful or delightful; for Jerome says in his letter to Paulinus which is to be found at the beginning of the Bible: “True friendship cemented by Christ, is where men are drawn together, not by household interests, not by mere bodily presence, not by crafty and cajoling flattery, but by the fear of God, and the study of the Divine Scriptures.” No more is it friendship for the virtuous, since by charity we love even sinners, whereas friendship based on the virtuous is only for virtuous men (Ethic. viii). Therefore charity is not friendship.
On the contrary, It is written (John 15:15): “I will not now call you servants . . . but My friends.” Now this was said to them by reason of nothing else than charity. Therefore charity is friendship.