"If 'love is long-suffering and kind' (1 Cor. 13:4), a man who is fainthearted in the face of his afflictions and who therefore behaves wickedly towards those who have offended him, and stops loving them, surely lapses from the purpose of divine providence.
Watch yourself, lest the vice which separates you from your brother lies not in him but in yourself. Be reconciled with him without delay, so that you do not lapse from the commandment of love.
Do not hold the commandment of love in contempt, for through it you will become a son of God. But if you transgress it, you will become a son of Gehenna.
What separates us from the love of friends is envying or being envied, causing or receiving harm, insulting or being insulted, and suspicious thoughts. Would that you had never done or experienced anything of this sort and in this way separated yourself from the love of a friend.
Has a brother been the occasion of some trial for you and has your resentment led you to hatred? Do not let yourself be overcome by this hatred, but conquer it with love. You will succeed in this by praying to God sincerely for your brother and by accepting his apology or else by conciliating him with an apology yourself, by regarding yourself as responsible for the trial and by patiently waiting until the cloud has passed."
Philokalia II pg 102