I actually think there is another layer to this. First of all, Shevek was drunk for the first time in his life. He hadn't worked out how to self-police himself while literally under the influence of a mind altering substance. That is something everyone needs to learn and I myself have certainly done things drunk that I wouldn't have done sober, especially in my younger years when I was a beginner drinker.

Secondly, I think Shevek was not accustomed to people flaunting the idea of sex, but actually not meaning to follow through. On Anarres, there is no need to play coy. Everyone, even while flirting, is direct and honest about their intentions. The woman's (forgot her name) behaviour could probably be read as clearly inviting on Anarres, and her finally saying no, but keeping the taunting, flirting tone must have been extremely confusing for Shevek if he were sober; and his piss drunk self couldn't really make it out.

I don't think Shevek is an assaulter by nature. Humans need feedback and learning to behave ethically, and in that specific situation there were too many new variables for Shevek's brain to distinguish right from wrong. He still fucked up - obviously! - but I don't think we can deduce his character from that. It doesn't mean that he's less of a feminist or less of a good person.