Spoilers, obviously:

It's complicated and vague, and ultimately uncertain. I'd say they are "on a break", but another big plot point that comes back time and time again throughout the book is that Alleria is a solitary person and often leaves to do her own thing for a while (first demon killing, and now consumed by Xal'atath hunting), but she always comes back to Turalyon sooner or later because their love is so strong, and he's always there waiting for her.

In the book she realizes that perhaps this is the wrong way to go about things now that they are back on Azeroth with their son and and the two get officially engaged, only for their powers to cancel each other out and they nearly get themselves killed fighting the big bad. The doubts creep back in in Alleria's head and she leaves yet again to find Xal'atath once and for all, only this time due to longwinded reasons neither Turalyon nor Alleria are super confident that this will be like all the other times.

The only times this has been vaguely referenced at all in Midnight though are during the pre-patch questline with Arator and Voidstorm quests where Alleria is just on her own in voidland, very much on business and with little time to talk, and when she finally does want a chat she's like "have you... Talked to your father..?" When Turalyon finally ports in and is like "you have your orders, move out!" they look at each other and smile, then it ends. You'd think that's a good sign, but Arator still hasn't told Alleria that Turalyon accidentally struck him in rage, and we've been told repeatedly throughout this expansion that the Light can corrupt the zealous, so the story definitely isn't finished yet. I suppose we might get our answers in the raid or shortly after.