Sex!?!

I need help! How would you feel if some other couple had sex in the bed you and your boyfriend have sex in. So I lost my virginity in my boyfriends bed a while ago and thats where we regularly do it so its really special. So today my boyfriend and i had his guy friend and his girlfriend over and my boyfriend and I left the room and we found out that they had sex in our bed. My boyfriend is 18, im 17 and his friend and girlfriend are 16. Idk how i should feel. I am kinda upset about it but idk if i should feel that way. My boyfriend said that his guy friend needed to lose his virginity and they couldnt do it at his house...