Rihanna‘s locking it down — she and Drake are  officially exclusive.

Multiple sources extremely close to the couple tell  us, Rihanna and Drake have gone from casually hooking up to seriously dating …  they’ve decided to give it a serious shot.

We’re told Rihanna wants to  spend as much time with Drake as her schedule will allow — because he treats  her better than anyone she’s ever been with. Not a high bar.

As we  reported, the pair have been  virtually inseparable while Drake’s been touring in Europe — we’re  told Rihanna has spent every single night with him since she arrived.

As  for Drake, he’s smitten — one source said “he’s in the best mood he’s been in a  long time.”