They will lean on you until they see fit to return to their Polish BF. They are masters of shielding things. She will have returned to her lad with all her romantic idealism and then think, once again, that the grass is always greener on the other side. I've seen it so many times.
I've seen it happen quite a few times, a woman from Eastern Europe ( not always Polish but very often ) simply "forgetting" to tell guys she meets in the UK that she's got a boyfriend/fiancee/husband ( lol ) back in Poland waiting for her and then just proceeding to go with the flow, one guy here, the other guy there, see what Boyo a does, see what Boyo b does, a shag here, a shag there and so on.
Such women aren't worth the trouble. If You, heaven forbid, ever marry her, rest assured that You'll be sharing that particular minx with at least half-a-dozen other gents that You'll never find out about.
Oh, if You're really flush with cash there's an alternative method of obtaining the heart and soul of an Eastern European woman:
Promise her 500.000 quid if she marries You and throw in that You'll kill Yourself if she stays with the other gent. Should do the trick nicely, according to the article above.