Why wouldn't my ex tell his best friend we broke up?

my ex ended our relationship three weeks ago because he wasn't feeling it. we are still good friends from what it looks like and I'm very friendly with his best friend still. the last time I spoke to his best friend he talked to me like I was still in a relationship with my ex. and yes my ex was present when this was happening. He made some romantic jokes here and there about me and my ex. my ex didn't say anything or tell his best friend to stop. Some of the things he said made me realize that my ex never told him we broke up.

Why wouldn't my ex tell his best friend we broke up?
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