It sounds a little passive-aggressive on her part, though. To me, at least, it does. Are you sure that he makes it clear that the nights he spends with you are designated YOUR TIME? And why does he have to speak to her for you? Do you feel awkward talking to her about needing some privacy when you're with him?
Also, nothing prevented you from saying to him when he got back, "Get over here, hon!" and asking him to come to your side. You're his girlfriend, that wouldn't have been out of line. I wonder why he didn't do that himself without being asked. Couldn't he have said to her, "Move over, Wifey, let me get in the middle" easily enough?
Is he afraid of her in some way? It's such a simple thing.
You may also want to figure out a nice way to tell her to buzz off, just in case it happens again. Like, "Oh, Metamour, would you get on the other side of him? I want to make the most of every moment I have to cuddle with him before I go home. Thanks!"