A Strange Conditional: "I couldn’t have talked to her that day if I never talked to her again"

In The Great Gatsby, thus pens Fitzgerald:

‘However—I want to see you.’
‘I want to see you too.’
‘Suppose I don’t go to Southampton, and come into town this afternoon?’
‘No—I don’t think this afternoon.’
‘Very well.’
‘It’s impossible this afternoon. Various ...‘

We talked like that for a while and then abruptly we weren’t talking any longer. I don’t know which of us hung up with a sharp click but I know I didn’t care. I couldn’t have talked to her across a tea-table that day if I never talked to her again in this world.

It's a conversation between the narrator, Nick, and his quasi-partner, Jordan, followed by Nick's commentary.

I'm struggling to interpret the conditional sentence. Does it mean,

I couldn't have talked to her that afternoon, even if it meant I would never see her again.

Or,

Even if this had been my last chance to talk to her, I couldn't have done it.

Or something else?

More elaboration on the possible dialect or register that would featur such a structure is appreciated.

Let's reorder this and take out some descriptors:

If I never talked to her again, I couldn’t have talked to her that day.

"if" here, meaning that we're making a supposition that the rest of the statement depends on:

Supposing/On the pretense that I never talked to her again, I couldn't have talked to her that day.

Which to me seems like this falls into what you expected--it's saying "Even if this had been my last chance to talk to her, I couldn't have done it."

I think what makes this so strange is that the "if" isn't a concessive clause (an "Even if"), so we get no feeling of "despite the fact" even though it seems to be implied. This lack of emphasis on the comparative "if" is what--in my opinion--makes this whole thing hard to parse. If I were to rewrite the sentence, it would look like:

I couldn’t have talked to her across a tea-table that day--even if I never talked to her again in this world.

Using both the dash and concessive clause to emphasize the conditional and make sure it's understood correctly.