Boyfriend thinks he found “love” note

Hello, so my boyfriend was on my docs and found a little story I recovered from trash about 2-3 weeks ago that I did not delete again. I had written it early 2018 while in a relationship with someone else but I never wrote it for anyone. It was just a sad story about a relationship at 16. I loved writing and would always express myself that way and sometimes they’d be sad. He believes I wrote it for my ex which is untrue and of course he doesn’t believe me. Says he feels hurt and disrespected that I would recover it and lie to his face when I tell him it was never meant for anyone. Well he wont budge. We got into a huge fight and honestly I don’t know how to fix it because he has it in his brain that I’m holding onto a past relationship. Honestly it was worded so good and I haven’t written in so long that I didn’t even think to rid of it. Now I regret it. I’ve apologized and explained the situation and he still won’t believe me, says I’m a liar. When I was younger I would lie about the stupidest things that were just unnecessary and I’ve grown and learned from that but seems like he’ll always believe I’m a liar. Guess I fucked up this relationship.