Eh, what's normal, really? Doesn't sound weird to me. A scientist recently released results of a study she conducted in which it was found that most women get turned on by images that suggest the promise of sex. So, enjoy it.
My only question about your situation is, why did the gf move in with you? And why after dating your husband for only four months? That is the part that strikes me as rather odd, premature, perhaps a bit foolhardy, and where I would wave a yellow flag, just to be cautious. You hardly know someone at that early stage, even if he is "in love" with her. You say you're new to poly - were you under the mistaken impression that poly relationships mean everyone all has to live together? Do you have another relationship yourself? Hope you don't mind my asking - I'm just curious.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein