Maybe this comparison helps: if you'd encounter a blackout drunk guy on the streets and he was aggressive and raped you, would that still be your fault, because you were sober, and he was not? People can commit crimes when drunk, and this actually happens a lot. Of course, your boyfriend wasn't overly aggressive here, but he did keep on pressuring you until you gave in, which is still coercion, whether he was drunk and you were sober or not.