There is no official confirmation for either. In the first film Sarabi obviously was still the queen but this doesn't necessarely mean that Scar thought of her as his mate.
In the deleted scene of Simba's Pride Zira says she WOULD be Scar's queen if Scar was still the king - but this doesn't necessarely mean that she ever was o that she even really would be. All that is saying is that she THINKS she would be. But it could be just her fantasy, encouraged por Scar choosing her son as the future king. As for why Scar would choose her son, there could be number of reasons. Not necessarely his personal feelings towards the mother.
So, there's no official fact for that exact detail. It's left up to fanfiction.
Personally, I don't think he had a romantic relationship with either of them.
