“When you have something to say, silence is a lie.” Jordan Peterson
When your friend is actively hurting themselves and you see it, to not do something is being complicit in their bad behavior. A real friend is not an enabler for their self destruction but instead will plant their feet and speak up for the truth, to even fight their friend if need be for their own good.
At work, not speaking up when the ethical boundary is being stretched is cowardice and is abetting the forthcoming violations. Turning a blind eye means you still know that wrong is occurring and you will carry that burden still.
In your relationship, silence will slowly kill it. Better to fight and bring the issues to the surface where they can be addressed than let them fester and poison everything.
Speak up. Speak truth.