Sorry, but this does sound like you are being used. She moves in with you after 6 months because she doesn't have financial resources? (I can't really ding anyone for moving in too quickly - I practically moved in with MrS the day we started sleeping with him and Dude moved in just as quickly).
The fact that she is not willing to tell her casual fuck-buddy(FB)/friend with benefits(FWB) about her other relationship is a big "red flag" for me. If she is willing to lie to him, what makes you think she is being honest with you? Some people are not willing to let their metamours meet but a ground-rule of "ethical nonmonogamy" (be it open/swinging/poly/some combination) is honesty - everyone should at least know of everyone else so that they can make informed decisions (regarding emotional involvement, safer sex, etc.).
Just my 2 cents.
(will PM you this same message)
Me: poly bi female, in an "open-but-not-looking" V-plus with -
MrS: hetero polyflexible male, live-in husband (24+ yrs)
Dude: hetero poly male, live-in boyfriend (5+ yrs) and MrS's BFF
SLeW: platonic girlfriend and BFF
Lotus: "it's complicated"
+ "others" = FBs, FWBs, lover-friends, platonic G/BFs, boytoys, etc.
My poly blogs here:
The Journey of JaneQSmythe
The Notebook of JaneQSmythe