Wickedwaterwitch,
If I were you, I'd get your friend to move her things as soon as possible or do as sobernow suggested and take them round. I'd probaly keep things short and sweet - no deep conversation.
Friendships change and this friend is now leaving you feeling drained as well as P you off with her politics. And she's never explained why she dropped you when you were going through a bad patch.
For that alone, I wouldn't feel guilty about ending contact, but I might be tempted to leave things open ended and keep my distance from her for now. 1, because you might bump into her if she lives close to you, so always good to be on civilised terms and 2, because when she's had her baby, she might change a lot. You say her boyfriend will not support her or leave his wife, and, let's be honest, she probably hasn't got the faintest idea of how hard life can be if you're a single mother. Guess who'll be in line to be her new best friend then? You probably won't want to take up the mantle, but possibly, motherhood may make her a bit more fair minded and respectful of you, so she's nicer company again.
If you think you'd like her a bit better if she lost the rosy tinted glasses about her partner, then you could stick around in the background for now. As in I like you but don't like your decision to have this baby.
If, on the other hand, you're positive she will use you rotten whatever happens, then wave adieu now. Once your mind is set that way, it's very easy to see if you are being used, and very easy to forget the friend who does it.