Stepmoms trust?

okey, so i have asked this question twice already, and just really want a wide variety of answers. On vacation in August, my bf and i went to the beach. (we were on vacation with his parents and mine who are best friends) he is 17 and i am 16. well, we got into a hammock, and before we knew it we were having right there....discreetly, i was on the bottom he was on the top. well my stepmom came looking for us and she found us..she realized what we were doing. she marched us back to the hotel, and there, she and my bf mom yelled at us for what seemed like forever. then my stepmom took me to her hotel room and ed me. She said that if i was going to act like a child then i would be punished like one...which i totally do not understand cause what child would be doing that? she was super mad, and now she doesn't trust me like she used to. I mean we were really close, we still are, but not the same as before. she grounded me for weeks and my dad agreed with everything.