I had a pretty long debate with my friend about his relationship. He was saying how he's stopped caring about everyone else because of how highly he thinks of his girlfriend. He's put her on such a high pedestal that now everyone else is insignificant to him. He's said that if she left him he'd have nothing left worth holding on to so I'm really worried about him. I even tried to drop a hint by saying something like "what if by doing this you are hurting other people who have been friends with you for a long time", but he said he didn't care about it. Whenever I tried to say anything his only argument was that I'd never been in a relationship so I don't know what it's like, therefore I can't have an opinion on it.

He thinks he is an outlier in the statistics, that it's impossible for their relationship to die. Even when I said it will inevitably change (like all relationships do in time), he was in denial and said it wouldn't. I'm really worried that if the relationship falls apart, he's going to fall hard, and I don't want to think about what he'd do to himself in that case.

I want to talk to him about it but I know what he's going to say, the same thing he always said. Should I talk to his girlfriend about it? We aren't that close but I feel like she'd take me seriously cause she knows me and him are good friends