“I'm on my own tonight.”

Your wife has gone to visit her mother and taken your children with her. You're at home alone, but you don't mind it. You're enjoying the peace and quiet. Your brother calls to say "hi", and you tell him about this. You start by saying:

I'm on my own tonight.

(be) on (one's) own

This phrase means to be alone. However, "be alone" sounds sad and lonely. "On my own" sounds like a happy adventure.