After 10 year they only keep in subtext all the relationship, even Vivio called her moms friends.
That depends on what source material you're limiting yourself to, and even then canon relationships can still be treated as subtext is the author chooses. Nanoha and Fate even moved together, started a family and married but we're not getting too explicit details on their romantic relationship developed, and sadly enough the other secondary couples with less exposition and screen time haven't had the chance to get close to the relationship level that Nanoha, Fate and Vivio reached. And by the way, I don't think Vivio or nobody has ever stated that her mothers are only and no more than friends, that would be a contradiction.