Is the questioner considered a sinner for shunning a person due to their bad manners and suspicions about their practice of sodomy and abandonment of prayer, and does the warning mentioned in the noble Hadith regarding the non-ascension of deeds and the non-forgiveness of sins apply to them?

Boycotting a companion for a worldly reason is not permissible, due to the Prophet’s (peace be upon him) prohibition of shunning for more than three days, and the better of the two is the one who initiates the greeting. As for shunning for a religious benefit, it is prescribed if you have advised him and fear being influenced by him. Scholars have unanimously agreed on the permissibility of shunning someone whose association brings a deficiency in religion or harm. Evidence for its legitimacy is the Prophet's (peace be upon him) shunning of those who lagged behind in the Battle of Tabuk. The preferred approach in shunning people of disobedience is to consider the benefit: if shunning leads them to abandon the disobedience, then it is better; but if it increases their insistence, then refraining from shunning is better. Boycotting due to disobedience is not forbidden and does not subject its perpetrator to the threat of animosity mentioned in the Hadith, as that threat is specifically for shunning due to worldly matters.