I don't understand how the insta fans came up with this nonsense theory of Malhar/Divya having had a romantic relationship in the past.
First of all, if would have come out one way or another as he isn't one to hide things from his spouse and expects the same in return... second, he's a one-woman-man and the only two women he's been involved with, were both his wives (though with Kalyani things are moving very slowly).
Plus, Divya addressed him as "Sir", not something you do to a boyfriend, more what you call your boss/mentor/colleague/senior at work.
And if they had wanted to do a SL with a third angle between Kalma who's a woman from Malhar's past, they had the chance during Ketki's track and didn't, or could have simply shown Sampu having a change of heart and wanting Malhar, and again didn't.
He just isn't the kind of guy to do these kinda things... though I don't rule out Sampu possibly in the future wanting him for herself and trying to come between Kalma, but I'm 100% sure he won't fall for it, if they go there.