From the relationship development between the two couples, there is high possibility the ending is fumi ending. There is not enough chapters left to force sakura ending, but if somehow airi decided sakura could just come crawling back to shinobu in the next chapter and shinobu respond by kissing her feet, we might get sakura ending by the final chapter.
Well, airi manage to fullfil the whole tag premise of grapara! even if she did it by taking execution of each tag one by one and not as a whole. And for the whole 130+ chapter that execution is pretty plain to be honest. mediocre comedy, mediocre romance, and barely ntr.
There is also possibilty of a tragic ending where shinobu lost both girls to ntr and give up on his dream then decided to return behind the counter selling condoms to sakura and fumi