[Grammar] You can't leave/be leaving me

[kadioguy]

(In Oxford Oxford Advanced Learner's English-Chinese Dictionary 4th ed.)

a bad dream
situation that is so unpleasant one cannot believe it is real

You can't be leaving me - this is a bad dream!
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Why is the example sentence in the present progressive?

a. You can't be leaving me ...
b. You can't leave me ...

What different effects do (a) and (b) have?

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I assume that the following can apply to (a), but I don't know what different effects (a) and (b) have.

Practical English Usage 3rd ed.

214

We use the present progressive for future actions and events that have some present reality. It is most common in discussions of personal arrangements and fixed plans, when the time and place have been decided.

What are you doing this evening? ~ I'm washing my hair.

I'm seeing Larry on Saturday.

We're travelling round Mexico next summer.

Did you know I'm getting a new job?

What are we having for dinner?

My car's going in for a service next week.
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(Source)

 

[Tarheel]

You can't be leaving me -- the person doesn't want to believe it's happening

You can't leave me -- permission denied!

As you can see, those are two very different statements.

 

[kadioguy]

a bad dream
situation that is so unpleasant one cannot believe it is real

You can't be leaving me - this is a bad dream!

Is the speaker suggesting that the situation is so unpleasant that s/he doesn't want to the listener leaving (i.e., leave her/him alone)?

 

[Tarheel]

The speaker (of that statement) doesn't want to believe it's happening. Thus the statement about it being a bad dream.

 

[Tdol]

Leaving here means ending a relationship.