Friends sister told Friend?

Ok if you read my post a while back it was this ----> """ K, I went to my friends house for a couple days, we met in school at the age of 5 (were both 20 now) but he lives with his sister & Monday night my friend went to sleep because we stayed up late the night before, but I went into the living room where they have the big tv at & his sister was in there but like 1 hour later after she was done watching the movie (I had my eyes close at this point trying to get some sleep) she turned the tv off & then she laid her head on my shoulder....After that I asked what she was doing & then she got really close up & kissed me...& that led to her grabbing my hand taking me to her room & us proceeding to have sex.... lol... (his sister is 22 btw)

Ok, but I'm worried because my friend is real protective when it comes to his sister....So like should I tell him....or should I let her tell him??

She said she doesn't know what she wants to do -.- """"""""""

Anyways I ended up calling her & we talked for a while but then she said she had to go....about 15 minutes later I get a call from my friend & he says "I'll ******* kill you if you ever talk to her or me again..." (So she obviously told him)

What do I do about this now?? I really like her & she likes me... :(