I'm going to tell my friends parents about her boyfriend they don't know about
Why would you tell your friends parents?
I want them to accept my friend's boyfriend.
It is wrong to out your friend if she is not in danger. You might lose you friend if she doesn't want her parents to know.
She will thank me in the end. I just know it.
Whether you think the situation will turn out fine or not, you should not go behind your friends back and tell her parents about a secret she may have.