My SO had a huge issue with trusting me at the beginning of our relationship because we had agreed on an open-ish relationship, wherein I would agree to tell her anything she wanted to know.
I keep a personal journal that includes stuff like me sleeping with chicks, so I usually hide it. I crafted an easily accessible but hard as hell to see way to hide it inside my stereo speakers. She knew it was well hidden and secretly ransacked my apartment looking for it. When we made the aforementioned agreement, I decided I didn’t need to hide it anymore and put it on my headboard, inches from where we both sleep. A few days later we had a fight because she couldn’t believe that I was willing to divulge whatever information she wanted to know, so she went through every nook and cranny of my apartment looking for my journal. She gave up and just kind of collapsed in an angry heap. When I got home I freaked out because she lied when she said she trusted me and I finally said that the damn journal was on my headboard and one of her midnight stealth farts would have flipped it open and onto her face.
After that she slowly began to accept that, yes, I do dirty things and, yes, I tell her all of them. The only other weird moment was when she went into my email and forwarded a few messages from a female (platonic) chum of mine to her friends. I had given her my password so she could see I’m on the level about everything, and I had also told her that I had been sent the emails, so it really upset me when she sent them to her friends with the message, “I had to break into Jason’s email to get these, let me know what you think. Does she want him?” Of course, her friends took the completely neutral messages and turned them into conspiracies of sin when it sounded like I had something to hide.
Since then, she’s come to accept that I really will just tell her all my dirty thoughts and actions so we get along just great now.