I'm speechless reading someone can say "it's his fault", "what did he expect" etc. His behaviour was rather stupid and naive; you can't trust other ppl be drunk next to strangers. But the only one AT FAULT is she.
However I'm guessing it's not that definite that she actually raped him. I mean, considering her character and what she has said that later, she might have just said that "they did it" to waver him and to try make him break up with Sumire. Which ofc is also nasty, but at least isn't a crime.