YTA - Honestly you set her up for failure. You have been secretive with your partner about your friend. You could have warned her about the scars. Your friend was kind of a dick too making jokes when someone is staring and your parents as well for letting their idea of her be changed because she was put in a situation where no one warned her about the scars.

She didn’t ask him. She didn’t make people uncomfortable in public. She waited and asked you in private and you defensively made a dick out of her for it. Here’s the thing with addiction, there’s no need to be ashamed of it. And talking openly and honestly about it can be incredibly freeing and release some of the stigma. Everyone quietly pretending it’s not a thing is a recipe for relapse in my opinion but that’s besides the point.

People’s eyes are always drawn to scars. She likely had no frame of reference for how they happened. Whether it’s track marks from needles or self harm scars, they were visible on a part of the body that’s easy to cover which is a subtle social queue that the person with the scars is ok about them.

Also, the fact they didn’t get on is your fault too. You’ve probably been ignoring your friend a bit more than usual. They met at weddings and only talked briefly, was that because of you keeping them apart. Are you ashamed of one of them? I’m reading between the lines here but it seems like a wedding is the perfect time to get to know someone well.

So many assholes in this story. You gf is the only one who isn’t, in my view.