Past back to haunt me

I’m in shock. My brother turns 43 tomorrow. Today he sent me a message asking about if I remembered something we did as kids (my brothers are 2 and 4 years older) I do not remember much detail and did not learn until later at school that it was wrong and stoped. Not sex but wrong all the same. Still bothers me to this day as well as other stuff. I froze and did not respond. When I checked again, he said he was asking because he wanted me to send him a picture of me in my panties. I haven’t responded but I’m so shook up right now.