How do you rebuild trust after a betrayal?

So my boyfriend secretly met up with his ex for a business project that he’s been working on. He knew it was wrong which is why he didn’t tell me. I found out after I saw his ex posted a pic of him online. I waited almost a month to collect myself bcs I didn’t want to immediately confront him while I was still an emotional wreck. I also gave him plenty of chances to come clean by asking him indirect questions, he never did come clean.

Finally, I called him out on it. Showed him the photo that his ex posted. He confessed and told me the story of what happened and how the meet up went. He knew that his ex is not over him yet, so he knew that she can probably cut him a good deal for her work.

I wasn’t mad but I was extremely disappointed that he didn’t even let me know in advance. Now I don’t even know if I can trust anything that he’s saying to me anymore… He said he’s willing to try and make it up to me but I don't know how I can even begin to try to trust him again. Help please.

How do you rebuild trust after a betrayal?
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