I accidentally saw my bf text with his ex-gf. "AITAH"

Hey so I have been dating my bf for 3 months now and I accidentally saw his text messages to his ex-gf. She texted him they can't be friends anymore because he is talking to me. They dated briefly in high school (he told me they dated for less than 6 months about 3 years ago). He texted and I quote "You are my light and my muse, please come back to me one day I will miss you so much, you are a star, you shine so bright you fit into my world perfectly, I never cry but I cried writing this to you, it feels like you are meant to be in my world, Ik how hard it can be trying to be friends with someone you love, if your question is "Do you love me? it's always I do, he also said "I'd kill, live and lie for you till I'm gray and old" Ik it's wrong to read other people's text messages but she happened to text him while I was on his phone and I ended up reading the rest. She responded, " I love you too and I always will, I hope she gives you the peace I couldn't, take care of yourself my love." I really don't know if he's over her yet because I have never dated before. But when I read this I had a gut wrenching feeling I have never felt before. I don't want to be the second woman because he couldn't keep the girl of his dreams. I still didn't tell him I read the text messages because I'm not sure what I would do. AITAH for all this? Please let me know what you think...help a girl out.