My boyfriend is insecure. How can I fix this?

My boyfriend looked in my phone while i was asleep and read messages that were years old. The messages were from me and a long time friend. I already explained that me and this friend had attempted to date but the chemistry wasn't there, that we shared a kiss but nothing more, and that this person was still in my life. He read the messages which CONFIRMED what I was saying. But he still is angry at me because he felt like I downplayed how intimate the relationship was. I do NOT like my friend as anything more than a friend and there are messages which clearly show that I broke it off because I didn't see him as more than a friend. Also, the messages are YEARS old. My boyfriend had asked me to block this person a few months ago and out of wanting to protect my relationship I blocked my friend of 13 years. I do feel like my friend had some feelings for me that possibly remained but it isn't mutual which I communicated to him and my boyfriend. My boyfriend is so mad at me he isn't even talking to me right now, and the main thing that frustrates me is that he isn't mad about anything inappropriate DURING our relationship because there is nothing inappropriate. I respect my relationship and love my boyfriend. He is mad about messages from before I even knew him. What do i do?

My boyfriend is insecure. How can I fix this?
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