I Could Have Back that Which I Treasured

Hi.
I was a bit puzzled over the structure of the sentence in red. Bob fantasized about the possibility of keeping his current job in Chicago, and commuting back and forth from home in Cleavland by air. And here's what follows it:

It would cost me more than my entire salary, I calculated, but in the fantasy I could have back that which I treasured, and still pursue the job I knew was right for me. In my nonfantasy world, the real one in which I was living and working, I would see Jack on those Chicago weekends and we would talk about where Allan was, and Chuck, and Dan, and what I wanted was for all of that not to have ended. ('And You Know You Should Be Glad' by Bob Greene)

The sentence in question is in red, and my structure breakdown is as follows:
[in the fantasy] I could have back that which I treasured
-"That which I teasured" is one unit >>> the one that I treasured
-"in the fantasy" is an adverbial that modifies the whole sentence.
-'Back' here gives out the meaning that he had once fantasized it and known he couldn't do it, but he fantasized it again.

I paraphrased the whole part as "in the dream, I could re-envisage my commute by airplane." Am I on the right track?

Why do you think it is 'that which' is used here instead of 'the + noun + which/that,' such as 'the dream commute which/that?

Thanks,

Hiro