Confirmed is a strong word. It's pretty clear that Bell and Ais will be together by the end of the series It's also really unlikely that something as big as their relationship wouldn't get a dedicated arc. I think the closest the author has come to confirming anything is him saying Bell's and Ais's relationship will start to really heat up when Bell reaches Lvl 6. (To be fair though I'm not even sure he said it I got that info from posts on here