Boyfriend sending nudes

I need advise…so I found out my boyfriend has sent a picture of his penis to someone else, he has told me it was a stupid mistake and he regretted it straight away and would never do it again. It was to someone he has never met before and she threatened to tell me so he made up an elaborate lie up saying he got hacked but then a few days later finally admitted it to me what he had done. I am still really hurt by it but I don’t know how I’m meant to react to it? Can anyone give me their thoughts on the situation? X