So for some context, I've never had a girlfriend and my dad believes that I've never been on any dates with any girls (because I've never told him about them) We don't talk about this stuff in the family and whenever I have been on dates I just tell him that I'm hanging with friends. So to get to the point, I've been seeing this girl for a few months now and I am going to ask her to be my girlfriend soon. I'm going out with her for a valentines day dinner and I'm debating whether or not I tell him I'm going on a date or just going out with friends.. I want to tell him the truth because it's only going to get harder as time goes on but I'm honestly not sure how to tell him that I'm going on a date with a girl. Can anyone help me here?

I'm 18 Male btw