Found my SO on Craigslist personal ads

A few years ago I (32F) caught my boyfriend (32M) on Craigslist personal ads where he had posted he was looking to get laid before heading home from work. I found it in his email account he left up on my phone after logging in and forgetting to close it. I don’t think I’ve ever gotten over it. To this day I don’t trust him, and I always wonder if he’s browsing sites like that. He never really talked with me about it, he just said he never followed through with it. Any advice on moving on from this or dealing with it so I can trust him again?