Ray J and Princess Love's toxic relationship hit a new milestone -- a wedding engagement ... with one big catch.
We're told the on-again, off-again couple want to stick together for the long haul -- they're already making wedding plans -- but only if they both stay sober.
It had been a rocky road for them, and we're told alcohol was a key factor in their frequent break-ups -- one of which led to Ray J taking back the Bentley he'd gotten for her.
Ray J actually proposed back in October with an 8-carat rock worth $130k, and sweetened the deal with a diamond-smothered Rolex ... once she said yes.
We're told the relationship is solid now that they're booze-free. One silver lining to all their squabbles -- it was a great source of material for Ray's new "Curtains Closed" video.