WHOA! This is big! We just realized the reason Hailey's been leaving church separate from Justin every Wednesday and why the married couple hasn't been together too much as of late ... they're living apart!

Or at least they might be ...

We spotted Hailey Baldwin leaving the Montage Beverly Hills on Friday without Justin -- which is normal, because even though the couple owns a residence at the luxe hotel, they don't live there anymore since they bought their first home together just a few miles away.

We've seen Justin in and out of the new manse plenty of times recently, but Hailey's been M.I.A.! The supermodel stepped out in an all-white look the other day -- an oversized boyfriend button-down over a white tank and mini-skirt that showed off her long legs. She hopped in her old Range Rover (NOT the couple's Lamborghini Urus that they take when they're together), and she spend off to a meeting.

Meanwhile, Justin's been getting some kind of intravenous therapy -- to help with a weak immune system and with his anxiety, we suspect. He's been at a Cedars Sinai-affiliated clinic multiples times a week, leaving with his IV fluid back on one arm, with a tube connected to his other arm, receiving a constant flow of liquid. WHAT IS UP?!