relationship with one of my dad's employees

my dad has his own business that is run out of the house and so all of his employees come here to meet up for the day and they often stay late into the night. I recently turned 18 and I have started talking to one of his employees. he's pretty cute but he's 26. we have exchanged numbers and we literally talk all day long and when we hang out I don't tell my dad who I am with. we have had sex a few times and I'm really like him. should I wait till it's more serious to tell my dad? or not tell him at all?