They were sort of one of the same person back then and thought they only had eachother before they became sacred beasts so yes
I mean romantically and sexually
Seeing as Hao mind controlled/brainwashed nagi in I think ch.14? It was mentioned that it was his wedding day(with Hao) before kotone came back. So 100℅ they probably used to like each other like that because one of the things about marriage is spending the night(as in having sex) with your spouse.
So something did happen between them?
I thought nagi just love him as a family
I would've thought so too but it was clear Hao loved nagi that way and he probably used to feel the same too since he apparently didn't like or approve of Hao's chosen one at first
I don’t think Nagi ever loved Hao as a lover. Nagi never had any indication he loved him like that even though there were plenty of chances to reciprocate Hao’s love. He didn’t approve of Hao’s chosen one because he is like a protective brother.
But their other friend which is the tiger said " he doesn't even realize nagi loved him" kindaa like that
Because he does love him as a family but Hao became obsessed and tried to force his love (romantically) on to Nagi which caused their relationship to drift apart and they become not as close anymore but Hao did not realise Nagi has always loved and cared for him just not in the way he wished for.
So nagi did love the turtle?