My boyfriend has been messaging girls on craigslist for hook-ups, exchanges pics... what do I do?

I love my boyfriend and he loves me. We have talked about getting married in the future, but nothing in stone.

A few weeks ago, I found his secret email account in addition to all his searches on CL on his computer. I confronted him about it and he told me it was unacceptable and he had no excuse, but that it was just for porn/entertainment and that he has never followed through or cheated. He said that he has been doing it for years, and basically never stopped when we started dating over a year ago.
I asked him if this was a far as it went, if he had other accounts, emails, had he ever sent pics or had a relationship with any of them and he said no.

A few days later, I found another email account and a few days after that I found pics he had taken of himself. I managed to hack into the email accounts and found only a couple of messages as he had deleted all the others prior to me finding all this out. There messages are as he described, simple requests for pics etc. I did find that he did research one girl & the 'meetup' link she sent him, which he found out to be a dating scam online, as most of them are. What of she was not a scam though? Would he have followed through? I can't see the search history further than one month, so I don't know if that behavior is typical as well.

He told me he never talked to a 'real' person or followed through with anything. He has been super depressed for the past 2 weeks, he wakes up crying some mornings wanting to hold me and tell me how much he loves me. I believe him and know that we have something very special, as we have known each other for a long time and our connection and relationship is special. He was lonely for several years prior to us getting together, and I know that this started out of basic need for companionship and low self esteem... it just never stopped once we got together.

I want to love him and I want to trust him. I don't know how to succeed in this though. Any advice would be appreciated.
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I should add as well that I have good reason to believe he has not cheated... without going into detail, but it involves work, schedules and transportation etc. There are definitely times he could have gotten away, but logistically it would be hard.
My boyfriend has been messaging girls on craigslist for hook-ups, exchanges pics... what do I do?
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