How do I tell my friend her crush doesn't like her?

My friend keeps telling me just because her crush talks to us on nights out that he wants her. But he is just being friendly. He's got a girlfriend and she thinks the girlfriend is jealous of her because he likes her and not his girlfriend. This guy is my friend and he told me he doesn't even know my friend's name and isn't interested. But my friend is insisting he likes her out of confirmation bias. I keep encouraging her to get a new crush or talk to another guy but she keeps saying he wants her. How do I break it to her nicely? She's a bit insecure about guys and guys attention in general so I don't want to upset her.
How do I tell my friend her crush doesn't like her?
Post Opinion