Cote, I'm going to tell you about a similar situation that happened to me about two years ago.
I had an ex boyfriend who got in touch with me via Friends Reunited. He was someone who had meant a lot to me but it hadn't worked out because his job had taken him to Hong Kong for two years. I wouldn't go with him because it would have meant taking DS1 away from his Dad.
Anyway, here was someone who remembered me as young and sexy... I was flattered. I felt that our emails were innocent but I did have a spring in my step and butterflies in my stomach, so in reality they weren't.
The emails got more intense on his side and I started to get a bit uncomfortable but didn't want to stop because of the way he made me feel. I told him that they were not the sort of thing that I would want my family coming across. Without any instuction from me, he set up another email account for me and sent the details via email.
At this point, I knew things were getting out of control. I had wanted to meet him, not really sure why, I didn't want sex or anything... maybe it was just because I had such fond memories.
I decided to tell DH. I was too late... he had been following the whole thing and the new email account was the last straw. The look of total hurt and bewilderment on his face is something I will never forget.
I am so glad that he told me. I might have gone on to make a really big mistake, whilst all the time convincing myself that it was harmless.
It took a good six months before I felt that he had forgiven me but I know that he occasionally checks my emails from time to time. I'm happy for him to do that, I just want to regain his full trust.
I tell you this because it sounds as though your DH has got himself into a similar situation. He may thank you for confronting him and stopping him from making an horrendous mistake.
Good luck, whatever you decide.