My first piece of advice would be to stop catering to her negative comments.
When couples are feeling hopeless, particularly the person who wants out, there is a lot of negative perspective on your history together. Walk away spouses say things like "I don't love you anymore" and "I never was in love with you" and "how can we fall in love again if we never were to begin with."
First, people fall in love with little to nohistory together ALL the TIME. How do you think love comes to life to begin with? The idea that you can never fall in love with someone who you weren't in love wiht before is prepostorous. If everyone has to have a romantic history together or they wont connect how did anyone get connected the FIRST time?
Don't cater to this ridiculous reasoning. Its just hopelessness talking. DR has a very powerful point in it by michele saying "Don't listen to anything your spouse says that's negative" Paraphrasing, but her point is that you can't cater to her hopelessness. YOU have to be HOPE FOR HER right now, don't nod when she says something negative, and DON"T argue with her or agree. Just be hopeful and SHOW it. Don't get into those silly conversations.
When she's hopeless just tell her you love her and that you will do everything it takes to get the two of you back on track. THAT will make HER feel more hopeful.
Acknowlege her pain, support her through that, but DON'T cater to the negative perspective and enable it. BELIEVE you CAN get somewhere with her. YOu MUST have had passion at some point or you would'nt have gotten this far. Just help her find that again. Don't agree with her it wasn't there, you are just aggravating her sense of hopelessness.
Read DR again, i had to read it several times before it started to sink in.