dads???sex???wtf dad???

Ok so i was at my bfs house today and we had planned on having sex while our families where talking and eating, but we told my mom we where gonna go look at something in his room bc he has a huge fish tank in his room, and his room is separated from the house its part of the garage, so we told my mom we where goin out there to look at the fish tank and my dad butts in and says you have 5 min , and im thinking wtf bc my fuckin parents cockblocked me, how tf do they know wht we where going to do, his parents are ok with it but mine aren't. Why is my dad so overprotective? I mean ive had sex before but they dont know but still why is my dad like this.