@Wrongreality25 With my sims, the romance bar tends to react differently with different woohoo partner couples.
With some couples, every time they woohoo, their romance bar goes into the red.
With a few couples, doing woohoo always makes their romance bar go into the pink.
I don't know what determines which way the romance bar will move.
In either case, though, if I wanted to switch the relationship to a romantic one, I'd had to use the "End the woohoo partnership" social first.