Interacting with a murtad

Q: I have a relative that turned to Christianity. He therefore is a murtad for more than 30 years and I refuse to associate with him. Some family members however associate with him as per normal. I even saw him recently in a masjid for his mother's janaaza taking part in the salaah.

I would appreciate if you can advise as everyone thinks I'm at fault as I must greet and interact with him to show him the beauty of Islam although he is a born Muslim. We tried in the beginning but he regrettably still practices Christianity.