[0] Australian Government Publishing Service's Style Manual for Authors, Editors and Printers, ISBN: 978 0 7016 3648 7
[1] The Canadian style: a guide to writing and editing https://archive.org/details/canadianstylegui0000unse
Formally, most comma use is an issue of style, not grammar, and style guides differ on when they should and shouldn't be used. The main rule that's actually a matter of grammar is this: commas cannot be used to join two "clauses" (phrases which could be independent sentences) without a conjunction.
There's a caveat where some style guides permit using a comma without a conjunction in specific contexts, but most don't.
The lack or excess of commas doesn't upset any reasonable person in the slightest.
And almost nobody writes sentences like "I love her and she loves me back" with a comma before "and".
A subordinating conjunction like if turns an independent clause into a dependent clause, so you don’t use a comma.
> And almost nobody writes sentences like "I love her and she loves me back" with a comma before "and".
In informal writing, people frequently leave out commas for everything but lists.
But it’s also very common to see it used “correctly”. In any kind of writing where someone would be expected to proofread what they wrote, I’d expect it.