If I want to be with a man as a wife and mother for the rest of my life than supposedly he is a dad to me.?

I do not get this do you? I only get with men I can see myself marrying, and spending the rest of my life with. According to others this makes him a dad. Unless I am a promiscuous women and give my body up to men, my future husband is a "dad", this I do not understand. My dad is not in my life by the way.