My brother is blackmailing me?

well im 17 and to put it simple a i was teasing around with my one friend on fb a few sexual jokes nothing serious or anything just jokes for laughs and well my I saw my bro coming over so I quickly exited out of our chat, and I was about to respond to her message back when my bro came along. I quickly exited out of chat but of course with my luck she sent a 2nd 'im and my bro saw a part of it. now he's threatening to tell our mom if I don't do all he wants >.>