AGONY: My son demands to see his father who abandoned us

When the boy was three years old, I re-established contact with my ex-boyfriend to play his role in his son’s life.

AGONY   FAMILY & RELATIONSHIPS

I have a 15-year-old son. His father abandoned me when I was pregnant.

When the boy was three years old, I re-established contact with my ex-boyfriend to play his role in his son's life. 

My ex-boyfriend denied being the father and I cut off all ties with him. However, my son is now demanding to meet his father. 

Given the way my ex-boyfriend behaved when I got pregnant and when I re-established contact with him, I am tempted to tell my son that his father died, which is not true. What should I do?