Is the failure to perform the Sunnah, while adhering to the obligatory duties, considered a sin, and how can one overcome the intense sadness and continuous distress resulting from a problem with a friend, despite supplication, seeking forgiveness, and reading the Quran?

Be diligent in frequent supplication and asking for well-being, and in observing the obligatory prayers, reciting the Quran, and much seeking of forgiveness and remembrance [of Allah] so that your heart may find peace. Be gentle with yourself and do not destroy it with grief, and strive for reconciliation between you two. If reconciliation is not achieved, do not distress yourself over it, for there are replacements among people, and in leaving, there is comfort. A Muslim does not sin by abandoning supererogatory acts of worship, but they should not be abandoned entirely. Friendship between a man and a non-mahram woman is not permissible, as it is a door to temptation and corruption. There is a consultation section on the website that can be resorted to for social problems.