Terrible mistake done!

I slept with my husband's best friend last week. I don't know I was so numb, now this guy keeps asking me nude pictures and ask for sex all the time or else said to tell my husband.

so I slept with him 4-5 times, in a state of bitter feelings.

he continues to ask for sex and nude pictures. what do I do? I'm fed up of waving my husband goodbye to office and then going to get laid.