German translation help

Hi all!

I've bought a rare silent film on eBay which I am planning to share online, since it's public domain and I like it quite a lot. It has German intertitles, though, so I am working on subtitling it in English. I'm getting along fairly well, but there's one phrase in the film I can't figure out. I'd love it if any of you could help!

The situation: a business-owning woman finds out that the man she's in a relationship with, whom she has also made co-owner of her company, is trying very hard to seduce her cousin. At this point she retreats to her rooms, obviously very upset, and after a while her dramatic swooning changes to anger and she exclaims "Das mir!"

I'm really not sure what to make of that - I was thinking maybe something along the lines of "How could he do that to me!" but I am very unsure. Any help would be great!

Thanks very much in advance :)