He is definitely in the wrong to have her staying for a month, without you meeting each other a few times before hand, and with so little notice.

I'd probably sit him down and explain how this has made you feel, and give him the reasons you feel that way. You'll probably have a constructive conversation, and he will apologise, and maybe you can try working a compromise out?

Stick to your guns on moving out and let him know that he left you no choice. As a compromise, maybe you could offer to come over and meet her for a drink for an hour.

He probably felt really nervous about talking to you about it, so he put it off, and put it off.

Shouting at each other won't really do any good, regardless of who is in the right and who is in the wrong. Talking is the only way forward and one of you has to make the first conciliatory move.

Good luck.