And another thing...Justine

[Mira]

It's not the sex itself that helps the condition, it's the feeding.  Sex is just bait and the channel the Raiths like to use to get the energy.  They can feed in other ways, like Skavis and Malvora do.  (IIRC, JB once said that in theory a WV could feed on the warm and fuzzy feeling from petting a kitten, though he added that the WV would probably sparkle if they did it, so he might have been joking about that).

The White Vampires feed on emotional energy, which is also life energy.  Justine in her manic state generates too much positive energy, in the depressed state too much negative.  The emotions are the energy and vice versa.  When Thomas feeds on Justine, it takes away those excess energies, leaving her more or less 'normal'...as long as he doesn't take too much or too often, of course.  In that respect, a manic depressive is the perfect prey for a WV with enough self control to limit their take, because they can be fed on without hurting them, and even to their benefit.

(Ignoring the potential issue of supersex addiction, of course.)

And yeah, once Thomas couldn't feed on her any more, one would expect that she would either revert over time to her manic/depressive state, or have to use medication to control it.  Which might be where Nemesis got its hooks in.

Do we know for sure that Justine's illness was manic depression? As we know there are more than one type of mental illness.  If Justine suffered from a form of schizophrenia for example, hallucinations possibly could be the perfect avenue for Nemesis to enter. Can you imagine if Justine was hearing voices for example how easy it would be for Nemesis to become one of those voices?

[g33k]

Do we know for sure that Justine's illness was manic depression? As we know there are more than one type of mental illness.  If Justine suffered from a form of schizophrenia for example, hallucinations possibly could be the perfect avenue for Nemesis to enter. Can you imagine if Justine was hearing voices for example how easy it would be for Nemesis to become one of those voices? 

I don't think we know the form(s) of Justine's mental illness, no (noting that multiple-diagnoses are very much a thing).  It's not clear to me that Jim does, himself.

I doubt Jim will specifically write it as "hallucinations" though -- that really muddies the whole "free will" issue, which is thematically-important to the Dresdenverse.

[Mira]

I don't think we know the form(s) of Justine's mental illness, no (noting that multiple-diagnoses are very much a thing).  It's not clear to me that Jim does, himself.

I doubt Jim will specifically write it as "hallucinations" though -- that really muddies the whole "free will" issue, which is thematically-important to the Dresdenverse.

Why would it?  You think that Nemesis cares about "free will?"  And though not by Nemesis, but by one of the Fallen, Lasciel was perfectly happy to use a hallucination, i.e. Shelia to seduce Harry into taking up a coin.  The taking of the coin itself might be an act of free will, but getting him to that point goes against his free will, as we saw Harry's reaction once he realized it.  Why wouldn't Nemesis use Justine's mental illness to produce hallucinations to fool her into accepting an Outsider take over of her person? Do you think Justine was really thinking clearly when she agreed to that?

[Talby16]

Why would it?  You think that Nemesis cares about "free will?"  And though not by Nemesis, but by one of the Fallen, Lasciel was perfectly happy to use a hallucination, i.e. Shelia to seduce Harry into taking up a coin.  The taking of the coin itself might be an act of free will, but getting him to that point goes against his free will, as we saw Harry's reaction once he realized it.  Why wouldn't Nemesis use Justine's mental illness to produce hallucinations to fool her into accepting an Outsider take over of her person? Do you think Justine was really thinking clearly when she agreed to that?

Most of the fallen try to erode their carrier's free will to make them into little more than slaves to their will. The concept of free will is important, but it can be challenged. We saw that with the whole Harry killing himself plot. One of the Fallen told him a lie which effectively altered his choice causing him to kill himself. Uriel stepped in to bring balance back in that situation. I totally believe that Nemesis would try to alter or override free will in order to make a more compatible host. I think that we get some of that with Sith's corruption. Cat Sith was fighting Harry in Cold Days until Harry started challenging him according to Winter Law and Mab's Will. We saw the conflict Cat Sith was going through. We saw Harry urging Cat Sith to fight the infection. Then, Nemesis seemingly took over completely overriding Cat Sith's Free will. My two cents at least.