Long story short ...

My bf has this female friend who hes known for about 4 years now. Last year she admitted to having feelings for him. He doesnt feel that way about her, so he played it off in a way to make her not feel bad. I saw the messages, and he didnt flirt with her or make it seem like he way interested in her at all. I trust him. But they're still friends, and I don't like it when they hang out. It makes me uncomfortable thinking about how she "liked" him. I know he wont do anything, but it just feels wrong in a way. Slightly disrespectful towards me... idk. Am I overthinking it?