I mean, my friend's relationship wasn't even the "throw the whole man out" kind exactly, it was the "you're putting in a whole lot more than you're getting out and it doesn't seem to make you happy" kind. And we did do a lot of "Maybe you should stop paying his credit card and doing his laundry?" and "when was the last time you two had fun together?" type advice, but nobody actually came out and said, "Hey, I think the relationship is over and everybody involved here would be happier if you broke up". (Turned out everybody other than her, including him, had been just quietly waiting for her to figure it out on her own. Didn't work.)

But also, yeah, that was a case where he's actually a generally nice guy we all liked but he really needed to not be in a relationship with the kind of person who would wear herself out doing his laundry and taxes for him. There are also cases where it's the other way around, the relationship actually seems fine it's just the guy is like nails on a chalkboard to you, in which case it's fine to tell her you don't want to spend time with the guy, just don't present it as a reason they need to break up and it'll go over a lot better.