EDITED: Desperate to save their TV show from cancellation, two feuding co-stars, an aging actress and a troubled younger actor, enter a fabricated public romance to boost ratings

I like the re-write, However; I would take out the line "...that soon turns complicated when..." and just insert the word 'but' This will help the flow of the logline and take out unnecessary wording.
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"Desperate to improve ratings for their TV show, an aging actress and a troubled younger actor enter a fabricated romance, but must outwit a tenacious paparazzo and vengeful ex-lovers out to expose them."

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DylanK nailed the feedback- you have a great premise, but a logline must set up the premise and also describe the main plot line or conflict.?So you've basically described the first 25 pages or so, what happens in the next 50 pages?

You don't even need to rewrite your logline, you just need to add to it- "Desperate to resurrect their failing careers, an aging actress and a troubled younger actor enter a fabricated romance but...[PROBLEM]"

I agree, this is a great premise. As for the logline, how about adding an antagonist.
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"After TMZ features her as the number one 'has been' of the 80's, a former TV bombshell enlists a handsome up-and-coming actor to engage in a fake, May-December romance to reinvigorate her career; but must outwit a tenacious paparazzo who's out to expose the fraud."
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Hope this helps, good luck with this!