little brother walked in on me and my gf

Andrea • lesbian
Ok, so last week my little brother (13yo) walked in when my Gf and I (yes I'm gay) were having some fun alone time. He wasn't supposed to be home and he came home early. Now comes my problem....he's been kinda a perv about it and asking a lot of questions that seem off (like asking us what we do). I also found pics on his tablet two days ago that were lesbian porn.  I want to help him understand that we are normal but without sexualizing the nature of the intimacy he witnessed. He's being quite immature and I want him to understand. Any help would be awesome!