HELP JUST PLEASE

So my boyfriend and I are extremely close. I have been through abuse with my dad and he has managed to get me through it. We both love each other endlessly. He treats me so good. He prays with me everyday and it is the best. A couple of months ago something happened. He goes through really bad situations where he gets in awful head spaces and i’m usually there to get him through it. We tell each other everything and talk to each other when something comes up in our head or if we are worried about something. I wasn’t around to text him and knock out of it. He is very self conscious. He is the person the anyone can come to and is the sweetest person I know, everyone loves him. He had 100% trust and were in everything together no matter what. Going back to these depression head spaces that he goes through, someone happened to text him about nudes when he was in this head space. He sent one. Which he has never done before or shown any sign before and in fact he has shown many signs of me being able to trust him. It was over kik, and right away he said he deleted it and blocked the account and everything. This was towards the beginning of our relationship. He told me but what he told me was that it was before us and it was only the top of his, not a full nude. Then, this person found his email and emailed him a threat saying that they will expose his picture if he doesn’t pay them. Then obviously he got scared and deleted the email, they found him on instagram and so he deleted an instagram and we now share an instagram. Recently he has been very upset and he finally told me the truth. I know it it cheating, but that wasn’t him. I don’t want to give him excuses or anything. I like that fact that he told me. He has been praying with me a lot telling god to guide me to make the right choice for me. I dmed this girl on instagram and she send me it and also my friend it. It isn’t good and this situation is really scary. I really want some advise.