Benign Salivary Gland Tumor (e.g., Pleomorphic Adenoma): This is a common cause of cheek masses, especially given the patient's age and the slow growth of the mass over several years. The size of the mass (2.5-3.0 cm) and its location are consistent with a salivary gland tumor.

Mucous Cyst or Mucocele: These are common oral lesions that can occur on the cheek, often resulting from trauma or blockage of a salivary gland duct. The patient's history of biting himself could contribute to this diagnosis.
Lipoma or Soft Tissue Tumor: Although less common in the cheek, lipomas or other soft tissue tumors could present as a mass in this area, especially if they are deep-seated.
Dental-Related Abscess or Cyst: Given the patient's difficulty eating and history of biting himself, a dental-related issue causing a localized abscess or cyst is possible.

Malignant Salivary Gland Tumor (e.g., Adenoid Cystic Carcinoma, Mucoepidermoid Carcinoma): Although less common than benign tumors, malignant salivary gland tumors can present similarly and have significant implications for treatment and prognosis.
Metastatic Disease to the Salivary Gland: Rare, but a possibility, especially if the patient has a known history of cancer. This would be a critical diagnosis not to miss due to its implications for staging and treatment of the primary cancer.
Infectious Process (e.g., Actinomycosis, Tuberculosis): Chronic infections can cause masses in the cheek area and have significant treatment implications if not addressed.

Neurofibroma or Other Neurogenic Tumors: These can occur in the cheek but are less common. They might be considered, especially if there are other signs of neurofibromatosis.
Granulomatous Disease (e.g., Sarcoidosis): This could cause masses in the salivary glands or other tissues of the cheek, although it would be an uncommon presentation.
Vascular Malformations or Tumors (e.g., Hemangioma): These could present as a mass in the cheek, especially if they are deep-seated and have grown over time.