I think my friend has a problem

For the past month my (prism warlock main) friend has gotten a weird obsession with doing the legendary difficulty of the Desperate Measures mission from lightfall multiple times every day. It's gotten so bad that when my other friend and I get Into an argument with him over destiny related things like which build is better or etc, he always says "have you ever soloed Calus on legendary difficulty", (he can't even do Phalanx Echo solo). He says that fighting Calus gives him pleasure for some odd reason even though there's harder soloable content but whenever he's the fireteam leader that's where he takes us. I don't know what to do and it's kinda getting weird so pls send help.