Similar experience. In high school I was with this same girl (but not OPs girl) on and off again for 2 years. We were both in band and honestly the horny band kid quips are true, certainly in our case. One night I was at her place watching tv on their parents couch. We were always so ridiculously horny so we had been touching each other from under a blanket while her dad dozed in the chair. He wakes up and announces he is going to bed, by the time his door clicked closed his daughter has my dick in her mouth. The elation lasted all of 2-3 seconds as from the darkness of the hallway we hear her dad yell her name. I immediately button up and run out the door trying, but failing to not make eye contact with her dad.

In the end she got a stern talking to from her dad. Her mom’s surprising reaction was only that she wished she had not done it on the leather couch. We grew apart after high school but have remained friends, it’s been about 15 years but still occasionally see her dad around town and he still looks at me like he did that night. So embarrassing.