SPOILERS:
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I think if you dump her once, the romance it over....and I've heard if you dump for twice, she is gone for good (although I am not sure about this one). You can check this by using Shadowkeeper, under the global variable JaheriaRomanceActive, if it is set to 1, you are OK; if it is set to 2, then it is a good romance ending (sort of); and if it is set to 3, then "reload" if you choose to pick her.
As for Nalia, I believe you will still get her side quest when you take her back into the party after dumping her. Don't worry, being head of keep and thieves guild won't cause you any trouble at all in this aspect, it might actually help you if this is REAL LIFE.
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Long live H22A1!!!!!