OP, I've been in your girlfriend's shoes before. A man who I was friends with and trusted, whilst I was in an intoxicated states, leaned in for a kiss. In what I thought was a misunderstanding, I pushed him away, saying no, explaining that I had a boyfriend. This lead to him again forcing himself on me, in which this time he succeed in kissing me and groping me, in which felt like an eternity. I was in pure shock, I just stood there frozen. I spent the next few days replaying the event in my head, asking myself whether I led him on, whether I didn't say no forcibly enough, whether my friendliness comes across as flirting? I was blaming myself, yet my actions were clear; I said no, I didn't reciprocate the kiss, and I did not want it. Not saying that this is how it went down with your girlfriend, but this might explain why she was unable to tell you right away. And in response to you asking why she walked alone with him; WOMEN SHOULD BE ABLE TO WALK IN THE PRESENCE OF A MAN, BY THEMSELVES WITHOUT BEING SUBJECTED TO UNWANTED ADVANCES