How can I trust him again?

My bf, for me, was the most amazing guy I’ve met. I don’t date, he’s my 2nd bf after my first one cheated on me. I met my first from school and when I ended the my first. I decided I’d rather be single and alone than waste time dating, however, I stumbled upon this guy, and we both had connection I can never explain. I won’t go into details but he is the sweetest & nicest guy I’ve met. I fell completely in love with this guy. He comes over to clean my place, cook for me and really show that he cares form me. I have tried to not look for anything about him because he makes me feel loved & cared for and for me, those were good enough and I don’t care about his past. However, one day I was home configuring one of my computers and his email popped up as one of the logins. I have seen his email in the past and could’ve accessed it but I refused to because I was so afraid I might see something that would hurt me. But then, I can’t explain what it was that made me open his email. I can say he’s pretty good at keep tracks or hiding because all his trash were empty, inbox are pretty cleaned up, sent items were clean up until July 2016 - this is where I found email exchanges from craigslist. I say he cleaned up his inbox because the posting verification from craigslist and pretty much anything from craiglist are not in his inbox, he must’ve just missed his sent items. The email exchanges were about him meeting with guys to do sexual acts. Emails even had organ pictures of the guys showing uncut etc and to meet at some motel.. I was so hurt, I was never even aware that these things existed in craiglist. I work in the IT so I could say I’m pretty knowledgeable compared to most people when it comes to computers but as I mentioned earlier, I didn’t want to look or search for anything because he made me feel love and I trusted him. I was so devastated and so confused. I asked him to come over to my place an we had talked, I first asked him if he’s got anything to say or confess to me (I wanted to give him a chance to admit) but he denied and said he had nothing to hide from me. I gave him clues about Craigslist and the hotel name - but he was getting upset and said he doesn’t know what I’m talking about. So I was forced to tell him what I found out - he was very upset first about why I had gone through his email, then, he admitted it. He admitted that he was insecure about his size and he had to go to CL to compare his size to other guy’s thing. He said he never went through it and never went to the hotel. He said this is something that is so personal and that he never had talked to anybody about it.I told him that if he is gay, I would still accept and love him but he said he realize that’s not what he wanted and that he couldn’t go through it because he’s not attracted to guys. He said he loves me so much and that he was sorry he didn’t tell me but he said that’s something he was so embarrass about — So I forgave him… The next day, I wanted to confirm he is telling the truth, but I found out that he DID checked into the hotel had his name and he paid via his credit card — this hurt me more and i was so crushed. I called him out of anger and said I don’t ever want to see his face ever again and to stay away from me. I was done with him.. BUT he came over to my work waited for me when I got off work and tried to talk to me, he begged me and cried and begged so much I couldn’t stand seeing him like that so again.. I forgave him.. Ever since then, he’s been really trying to show how much he loves me and cares for me. He spends more time with me and calls me all the time..How I wish I could completely erase what he did but I can’t.. It keeps bothering me and now I go to CL looking for posts that may be created by him.. I have brought it up to him how much it bothers me and he keeps re-assuring that I have nothing to worry about and he loves me and I complete him etc..It crushes me too to feel this way because I do see that he’s trying but idk.. I have read about guys who hide these feelings and have secret affairs. Most postings I see in CL are guys who have gf and wives & kinds who want to be discreet and how I feel so sorry for all these girls they’re with. It hurts me so much thinking that I might be one of these girls, I’m with a guy pretending or wanting to be straight but have secret affairs. I need help :( I have bee consoling myself, reading up on things but its been really hard for me. I can’t even tell my friends about what I found out about him because I know the moment they find out, they will tell me to leave him.. At this point, I know I love him but I’m not too sure if I should be with him knowing that I have all these thoughts that he might be having secret affairs or hookups with guys..idk I’m desperately seeking your advice.
I appreciate any advice anyone can provide.

The question you need to ask yourself is, are you ok with him meeting men off craigslist for sexual favors? He will continue to do that, regardless of how much he says he loves you and tells you he never intended to do it. Clearly you had some instincts telling you to look through his email, and you found out more than you wanted to. But now you do know. You are well aware of his behavior, and you have 2 options: 1) End the relationship and move on; or 2) Accept his behavior and love him anyway. You cannot change someone, and you cannot make someone do anything they do not want to do. Unless someone truly wants to stop a behavior, they will never stop. If he knows you will get upset and threaten to leave him every time you find out, he will hide it from you. He will get better at hiding it from you and you will never be able to trust him. I really don't think he will stop meeting guys off Craigslist. He may not be gay, he may be bisexual or simply curious, but the point here is that he has cheated on you, and most likely more than once. I think you need to take some time to really think about what you want, and whether or not this is something you are willing to tolerate within your relationship.