Do I need to use a comma before "but" in these examples?

I am a native EL speaker, but struggle with commas.

I remember being taught - at school - that they are just used as a pause when it is natural to pause. This I did not understand (slow sentences contain many "pauses" when we stress time syllables). Be sure that a comma adds clarity.

Usually, I use commas either to join independent clauses (avoid comma splices), or to add parenthetical information, "an explanation or afterthought into a passage which is grammatically complete without it" (its root is in "put in").

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So (and forgive me for my additions to it):

I pull you in, but don't you get too close "don't you get too close" is an independent clause

I love you now, but will not tomorrow is 'now' meant just to indicate the present tense? If so, use a comma, because the parenthesised phrase does not change the meaning of the rest. You might read it as an explanation (I love you now only because you won't outstay your welcome)

It's wrong to steal, but not to borrow Same again; it seems like an afterthought this time

So they all seem correct. My current rule of thumb is that parentheses do not change the meaning of the rest of the sentence. You can see that obviously in appositive phrases:

The capital of France, Paris, is a beautiful city.

perhaps who you are speaking to does not know what the capital of France is called, but that makes no difference. The information you have added, that Paris is the capital, is not already included in the rest of the sentence.

I hope that helps, and I add the caveat I am just a native speaker, no grammarian.