My husband made me feel un-sexual when I was pregnant, but never in a purposeful way, more to do with subconscious avoidance which he felt awful about. If he had ever done something like that he'd have been sleeping on his mum's couch til he knew how to properly treat me.
It sounds to me that either she is just a rubbish, disrespectful girlfriend (whether drunk or not, that's no excuse), or she's punishing you in a weird twisted way. I know you were on-off, but she may view it as cheating, and the baby being the result of that she's taking it out on the bump if you know what I mean.
Either way, there's something underlying her behaviour. I suggest having a proper, honest heart to heart, or even better go to couples therapy. That kind of attitude to another human being is not acceptable around a child, it's abuse plain and simple. It can affect the way a child thinks and acts towards others if they are brought up in that kind of environment.
Sort it asap or get rid, not acceptable in the slightest xx