Help, I feel replaced!!!?

My daughter no longer lives with me and she is now living with her mother and boyfriend, my daughter is 4 and is already calling him daddy, this only bothers me because she plasters it on the internet with pictures of the both of them saying look at ariel and daddy. there not married and my ex-wife totally approves of her calling him daddy, I have already talked to her about it but she is very stubborn, I feel replaced and very sad, what should I do????