my step dad saw me giving my boyfriend a blowjob...

Okay so I need some opinions. My parents are pretty strict and have made it clear that they do not want my boyfriend and I having sex in our house. I try very hard to follow this rule however sometimes it does happen. My boyfriend and I both just finished our freshman year of college and we are both about to turn 19 and have been dating 4 years. So we are adults, we aren't children. We have both moved home for the summer. So the other night at dinner, my step dad said that the other night he was walking around outside the basement door and he saw me giving my boyfriend a blow job. And how that's completely unacceptable because "the no sex rule includes oral sex". I was so mortified talking about that stuff in front of my mom who just sat there silently like she was so disappointed in me, and I felt like a huge slut. I understand the respect part and stuff but I've walked in on my parents having sex before.... I get it's awkward and I'm sorry for that part of it but is it really fair of me, as an adult, to be in trouble for this?? Is me giving my boyfriend a blowjob really that big of a deal that my parents think they have to disclipline me at the dinner table and embarrass the hell out of me?! I am sorry this is so long I just need some answers. Thanks!