i think he thought it was the most pragmatic and most practical way to make sure that he wouldn't belong to mab completely. or it was his way of cheating mab out of her new winter knight.

Except that Harry could not have been in his right mind when he decided that. Since no mention was made of Molly changing anything except Harry's memory of the conversation with Molly and the call to Kincaid, I assume Molly did not try any deeper tampering. Therefore, when Harry told Mab that he would not commit suicide, he really believed that he would not, or Mab would have known. And Harry would have been operating normally when telling that to Mab, only missing the memory about committing suicide. So, if Harry in his right mind would contemplate killing himself to escape being the Winter Knight, Mab would have seen it in his mind.

Hmmm, I am not sure if I am explaining this well. My point is basically that Molly apparently did very little to Harry's mind -- she only erased a memory. So when Harry told Mab he wanted to be the Winter Knight, Harry was basically operating in his normal mental capacity. And Mab seemed to believe Harry that he would not commit suicide. So, that means that Harry ordinarily would not even contemplate suicide to escape from Mab.

The whole situation is rather odd. Unless Molly did a lot more to Harry's mind than just erasing a few minutes of memories.

Some of us have been saying for years now that she just had to willingly make love to someone else and then Thomas could touch her.

Not the best choice of words. Justine needs to have sex with someone else. Making love, not so much, since that might put the protection on her again.

I think Demonreach would hardly perceive a tree as a parasite: a parasite lives off its host without giving it anything in return. The tree takes energy from sunlight, turns it into sugars, "fixes" nitrogen in the soil, etc. What's more its dead body then nourishes the soil. The tree is much more akin to an organ of Demonreach's than a parasite of it.

That all assumes that Demonreach cares about fixing nitrogen in the soil or nourishing the soil. I don't know why it would care about that. Is it an environmentalist demon? A farmer demon? I don't think so.

Justine was really physically and mentally hurt by Thomas' last feeding. It may have taken this long for her to recover fully, and be concerned about Thomas. He was taking care of himself pretty well for a while, until the Skinwalker, and I'm sure it took time for him to recover from that also.

No, Justine was recovered enough by Turn Coat, if not earlier. I'm thinking of the time they met in the nightclub, in particular. And by the beginning of Changes, Thomas was certainly recovered enough from the skinwalker. And there were probably other opportunities. I think Jim just did not think of it until recently.

Except that parasites tend to not help the host or respond to its demands. When Harry reached through his connection with Demonreach, the trees obeyed his wish to dump...what was hiding in them?...in Turn Coat.

That seems an unimportant distinction. What do you think Demonreach should call the tree, if not parasite? My woody thrall? 

It seems that the majority think that the parasite is Lash. I certainly hope that is just wishful thinking and the majority is wrong, because that is really lame. I hope that Butcher would not write something so contrived.

Dresden was shot in the chest near his heart by someone who does not miss. So there was some major heart damage. If the blood circulation was maintained by a beating heart, then Mab must have healed his heart almost instantly. And Mab was apparently providing "breath". If she can do all that, then causing the heart to beat is trivial. On top of that, the freaking tree can somehow magically grow conduits into Harry's blood vessels. If the tree can magically do that, it should be easy for it to also circulate the blood. Either way, there is no need to involve Lash to circulate the blood. If Butcher does write Lash into there for no good reason, then it is just lame. I hope he does not.

There's only one such being who has been in the position to know Harry in particular that well. Lasciel's Shadow.

I think you are making a big assumption there -- you are assuming that the entity must "know" Harry and that such a process requires past association. But an angel-level entity may be capable of reading Harry's entire mind instantly, so it could "know" Harry even if that was the first time that it had encountered him.