Why his exopthalmos only in one eye? Is this dangerous or can still be controlled? He did orbital scan but result says autoimmune tumor.

Orbital Pseudotumor. Inflammations around the eye can look like tumors and are called orbital pseudotumor. Orbital pseudotumor can affect one or both eyes of relatively young patients, usually 50 years old. They are not cancer. Ctscan shows diffuse infiltration of the orbit, an inflammation of the eye wall (sclera), and/or t-sign (with the optic nerve). Pain is common. The disease rapidly improves with oral steroids.
Depends. This could be many autoimmune tumors. This is not good, you need to be working with a good ophthalmologist. Depends on exact etiology on your concern for controlling it. Sorry i can not give more help! you need to be under the care of a doctor directly!