That ship is sailed (pun not intended), let's move on. Anything about it should've been addressed by Tini Howards early in Excalibur. Unfortunately, TH thought that the Queen Elizabeth AU was enough (spoiler: it wasn't).
Anyway. Now it's too late to return to explain anything about them. Anything unresolved between Betsy and Warren should've been resolved at the start of the new era (Krakoa).
Betsy has moved on (Warren likely too, we just didn't have much panel time with him in Krakoa era). At this point, having them address their past or status would be unrespectful to Rachel (and her role in Betsy's present), IMHO.