Perhaps you're thinking of Gingetsu/Ran from Clover? I'd say they're not quite canon-lovers, though I love them. Less there than Fye/Kurogane, definitely. They live together and have a whole slew of commitments to each other, but there's no real "yes they are a couple". Because CLAMP.

I think it's spelled out that they are each other's Special Person or wtfever CLAMP euphemism you like. But what that means is super fuzzy. Even love and marriage are all over the place - I wouldn't say Hikaru canonically romantically loves Eagle AND Lantis AND all her friends, but she uses those words for them all in the manga.