In the .hack//G.U. novels, Tomonari [Kuhn's PC] mentions that he and Mai had continued dating after high school by email and gradually drifted apart as their interests diverged before breaking up. Mai went on to volunteer abroad in places like South Asia and Africa, while Tomonari remained directionless and living in Kanazawa.
The breakup had a lasting effect on Tomonari, who years afterward, still regrets messing up his only "real relationship".