Got caught up last night with something else. Just reading now, and seeing the latest developments.
I know how your stomach will just knot up when this kind of stuff appears. I'm sorry to hear that! I think you are right about the fact that somehow you will need to regain trust in him to move forward and you will need his help for that. Right now, he's kind of sabotaging this process and it takes a long time to get past these things. And you have told him that it sounds like.
Your gut telling you he's not cheating is already proof of some level of trust from your side. However, I can completely understand how your stomach just sinks into your shoes when you see these emails. I guess in the end it is about BF understanding what you consider inappropriate contact.