终年不遇承蒙不弃
[zhōng nián bù yù chéng mĕng bù qì]
It reflects on a relationship with someone despite rarely seeing each other ('meeting once in a blue moon'), still maintaining this connection thanks to the grace (the tolerance, kindness) of the person. This signifies gratitude and the value placed upon such unwavering relationships over a prolonged time without physical contact.