You need not wonder whether you should have an unreliable person as a friend. An unreliable person is nobody's friend.

When friendships are real, they are not glass threads or frost work, but the solidest things we can know.

Amicu certus in re incerta cernitur'

[A true friend is a friend when in difficulty]

Wisdom is when you understand what, previously, at best you only knew.

A certain person may have, as you say, a wonderful presence; I do not know. What I do know is that he has a perfectly delightful absence.

Teach honesty by all means - you do know what it is, don't you?