Am I in the wrong?

I saw my boyfriend still has a note from his ex hung up in his room of her saying I love you babe. He’s brought her up before in conversation but says that they are just friends now, but they dated for 3 years. The ex also grabs dinner with my boyfriend’s mom from time to time and he says that it’s just because she’s like part of his family, and that I don’t have to worry.
She’s in a new relationship, so I don’t like see her as something I have to worry about, but I don’t think my boyfriend is as over her as he claims. I feel guilty for not trusting him. But the love note being brought with him when he moved to this town and hung up on his wall feels like a meaningful gesture. It just makes me feel sad like he’ll always be comparing me to her.