Commentary on Meditations: B1.13

13. From Catulus: not to spurn a friend's criticism, even if it may be an unreasonable complaint, but to try to restore his usual feelings; to speak of one's teachers with wholehearted gratitude, as is recorded of Domitius and Athenodotus; and a genuine love for children.

not to spurn ... usual feelings - it would seem the advice and lesson here is that friendship is greater than the friend's criticism (of you).  the way i read this, is we ought to look past shortcomings and "bad behavior" of our friends.  this is not to say we should associated with bad people and ignore all the bad they do, rather we should associate with good (virtuous) people and on occasion, they may not be perfect and we ought to overlook it.

speak of one's teachers with ... gratitude - parents, teachers, mentors, supervisors, managers - they do so much to help us.  we should respect them and be grateful for them.

genuine love for children - similar to jesus' admonition; we should love children - they are humans who are learning.