Boyfriend's Sister butting into our relationship

My boyfriend and I have had a tricky road with doing things long distance but we've finally both decided to get engaged and he's planning to move to my city.

We recently got into an argument where he did something he promised me he wouldn't, so naturally I got upset. His sister has always been a negative influence in some aspects of his life (my opinion) for example, she tried to convince him to do drugs with her.

My boyfriend tells her all our fights as he "needs someone to talk to sometimes" which is frustrating because he only tells his side of the story so she sided with him every time.

She called me over mine and my boyfriends last fight and I told her I don't approve of what she does but I won't stop her because it doesn't affect me. She doesn't need my approval.

She replied to me that I was rude for telling her to stop intoxicating herself. And yelled that I was controlling and can't tell my boyfriend what to do. She went on saying I should accept his terms because she doesn't want us to break up. I was so annoyed and angry because it doesn't involve her.

Eventually my boyfriend and I talked and we hashed it out. But she's pissed so I apologized to her because I don't want to fight with my future sister in law. But she's yet to reply back and is still mad. My boyfriend thanked me for apologizing to her. I personally felt it was unncessary to do so but I took one for the team lol.

I don't know how to stop her from getting so involved in our business. She's older than both of us but she still should stay out.

I'm just looking for an outside perspective. And some insight if anyone had any similar situation.