Yeah, I reread that section last night. Harry's subconscious first points out that Lara has many good points and that it could work between them. Then his subconscious further points out that Thomas and Justine were happy, then further points out why Lara's kiss didn't burn him. Calls into question if it was really true love between Harry and Murphy? Then adds the most important point, it's about balance. That's when Harry throws the glass against the wall. Balance, that is the key, and that's what haunts Harry in his grief more than anything. Was their relationship one of real true love? Or more of codependency? I think Harry is wondering too.
Why do I say this you may ask.
1] The soul gaze or lack there of, not until she was dying and nothing found out how she feels on the whole. I think Jim did that on purpose so we'd wonder, and Harry also wonders. Harry isn't really the most self confident guy, in some things he is, his will, power, etc. he is very confident. However his confidence in his past romantic relationships? A little shaky, so that hint of doubt.
2] Have you noticed that Harry really depended on Murphy's judgement, more than his own. In Cold Days she refused to give him back the Swords though he was appointed their Custodian, not her. She convinced him that somehow she was morally superior or gave that impression and he wasn't especially because he felt doubt since he was Winter Knight now. Even Michael told him this was something she took upon herself, and he went along with it. He tried to tell her not to bring the Sword of Faith with her when they went to confront Nick. She did anyway, relying on her judgement, not listening to Harry. Okay, you could say it was out of love, but it also was out of arrogance that she knew better. My point, one sided, and Harry went along with it.
3] As Mab told him in their confrontation, when Harry blames her for the banner which enabled Murphy to enter the fray though she wasn't physically up to it. Mab points out Murphy made that decision on her own, yet again ignoring Harry. Yeah,yeah, Harry's fear for her, over protective, yada, yada,yada.. However his judgement in this case was correct, but he still went along with her. No discussion as equals, no compromise as equals would do. What I personally found annoying about Murphy since Changes was she was sounding more like Harry's mom than an equal. Harry also became increasingly dependent on her judgement, that's why I say it had become a codependent relationship, which can be mistaken for true love. That's what was feeding Harry's guilt during the worst of his grief, why he felt responsible because he never really spoke up when he should have and it cost Murphy her life.
Back to Lara and Harry, that kind of dependency isn't there! Even when Mab was happy as hell because she thought Lara was completely dependent on Harry now. That wasn't the type of relationship Harry wants, and I think his subconscious could explain it to him now very well.
There is one obvious flaw with your analysis. Explain why Lara got burned when she touched Harry when they broke Thomas out of the castle. A codependent relationship shouldn't produce that effect. (Unless it would, but that seems unlikely. I think it would undercut the very idea of true love protection.)
I suppose you might counter that the true love Harry and Karin felt for one another ended when Harry fell into codependency when he accepted Karin's judgement for his own. But did he? I'd have to reread that part of BG again, but I remember Harry leaving Karin behind. She got on her Harley on her own and rejoined the battle on her own. What was Harry going to do at that point, forbid Karin from remaining with him? Maybe, but according to Ms. Gard, Harry would have died if he had done that.
I don't have an issue with your analysis of Karrin Murphy herself. I think we are largely in agreement that as a character, Murphy started to go off the rails in Cold Days. To get to the heart of the matter, I don't think Jim did a very good job of writing her after Ghost Story. At least in Ghost Story we could see that without Harry, Karrin Murphy was starting to become brittle and was on the verge of cracking up.
In Cold Days and Skin Game, Murphy would have been made more sense and also would have been far more relatable if her attitude had been something like, "I know your not alright Harry, because the same look I see on your face now, I saw in the mirror everyday while you were gone." Instead of acting in an accusatory manner, Murphy could have been the character who understood that even though Harry suffered severe emotional trauma, recovery was possible because she was recovering. I think it would have made Murphy bringing the sword with her in Skin Game a much more excusable offense. I huge mistake but an understandable one. Plus, it would have seemed a far less arrogant decision.
Maybe this is a problem that can occur when any author is attempting to write such a large number of novels in one series. Many people think continuity errors are where a series like the Dresden Files will start to go wrong. That can happen, but perhaps another and maybe larger problem is character logic and consistency start getting lost. As I understand it, Jim has a one or two page outline that he started with ideas for what would happen to Harry in each novel. According to one description of it I have heard, it is a very simple description of events that will happen in each novel. Dead Beat might have an entry that reads, "Harry must stop three necromancers from making one of there number into an immortal demi god. Harry will learn necromancy and raise the spirit of a 67 million year old T-Rex in order to fight the necromancers." Nothing about how Harry and supporting characters will grow or progress through each novel. Without such an outline some characters behavior may become illogical and, or inconsistent, just like Karrin Murphy became.