help!!

I'm currently going through a divorce and my EX & I have decided to see other people. We have a handsome 2 year old and he knows who Daddy is.. BUT today I heard my son call the guy I'm talking to Dad.. usually he calls him by his name (to the beat of his ability.) Now the guy I'm seeing said my sons has been saying that the last couple of times we've all been together but it doesn't bother him. I don't know what to do or how I should feel. After I heard it I immediately corrected him but still !! I need some advise 😬

 (please nothing negative)