My partner and I split up whilst I was still pregnant (he cheated on me.)
He generally has her on the weekends. It works for us because he works irregular shifts so would find it hard to look after her during weekdays.
Anyway, I started dating someone when my DD was 6 months(ish) and she is now 2. He moved in after a year and is now quite a bit part of DD's life.
DD calls him daddy, and I always say to her "no sweetheart, that's not daddy thats X "
I genuinely think the word daddy just means man to her, because I didn't introduce my partner to her until a month before he moved in. And my ex was the only man that she saw on a regular basis.
She even calls my dad daddy and last week when I was having coffee, she pointed to the man on the next table and said daddy.
I correct her, but she's two so I don't think she quite understands what I mean.
My ex came to pick her up last weekend and she called my partner daddy and my ex was clearly very upset and told me I was being cruel and vindictive and shouldn't let it happen.