[M] First time got walked in on. has tl;dr

I [M] was talking to this girl for a few months and we decided to meet at a part. Since it was summer we decided that we should go swimming at my house( In undergarments). As teens do we started kissing in the pool for a good 30m then we started getting kind of agitated because the water was drying out skin out so we decided to go inside. I plopped on the couch and at first she was unsure of herself because she “thought I would laugh at her”. I reassured her and we started to take our undergarments off. We’re both completely nude and I hear the garage door open. I start to panic as my dad wouldn’t be very happy to find out i’d lost my v card. I shove her into the bathroom then the door from the garage to the laundry room opens and i’m face to face with my brother. I can only imagine the thoughts going through his head seeing his little brother 100% nude with a raging boner and clothes strung all across the floor. He asked he “is anyone else here?” I say “yes” He says ” OK where can I go?” I said “your room” and with that he was off. I give my gf the all clear and we go back to the park. She broke up with me a few weeks later.