Perhaps you "should" have fought him off, but it's very very normal for people, all people, to freeze in a situation like that and not know what to do or how to feel.

It's just totally abnormal and your mind like short-circuits. It doesn't have anything to do with the weed.

If you feel like you have a problem, then stop. It's that simple.

But I wouldn't take your behavior in this situation as too much of a factor - it's just too bizarro to go on.