Who would have EVER guessed Playboy model Shauna Sexton's 15 minutes of fame would be dragging out this long!

Sexy Sexton wore a stunningly low-cut top, skinny jeans and leopard-print ankle boots to visit her pal Ben Affleck in rehab on Sunday. She even brought along some supplies ... too bad it wasn't In And Out burger, they're favorite!

The 22-year-old appears to be totally faithful to the 46-year-old actor while he completes treatment for alcohol addiction at The Canyon luxury rehab in Malibu.

In addition to Sexton and Affleck's relationship having an unexpectedly long shelf life, so does Ben's commitment to treatment! Most bookies probably would have placed odds on Ben not making it a full 30 days, but Affleck's coming up on a month in rehab in a few days now. Maybe he'll stay even longer!

But by the looks of Ben's face this morning as he arrived home for his morning work out, he's getting tiiiired of the grind ...