What should I do?

I came across something that my lover wrote about one of his best friends, it was basically saying that he was in the car with her and he realized that they'd never get to be together.. then when I confronted him he lied to my face and said it was about me.. he ended up telling the truth but he said that he hasn't felt that way about her for 4 years, but he just wrote that a couple of days ago. I don't believe him and I don't know what to do. Why would he be thinking about it or even writing about it if he hasn't felt that way about her in 4 years? Also is it wrong for me to not want him to see her anymore? Also this is the same day that we found out that our unborn son will have to have surgery when he is born on his esophagus and heart. It's just been a really hard day. He says he lied bc he didn't want to hurt me more?