"He is my future husband."

Translation: Αυτός είναι ο μελλοντικός μου άντρας.

[Stergi3]

Two accents when σύζυγος is followed by a posessive μου, σου, του etc, as there is a major rulein Greek, no word takes accent before the third syllable, and there posessives are considered as one word with the owner.

[SophiaMees]

Why is άντρας excluded from the possessive construction?

Is there a reason you wouldn't say ο μελλοντικός άντρας μου?

[Gabriela-X]

ο μέλλων μου άντρας - was marked wrong

[D_..]

For some reason that sounds weird... Ο μέλλων άντρας μου on the other hand sounds fine. ¯_(ツ)_/¯

[Gabriela-X]

For your native ears maybe it sounds weird , but for mine sounded just fine :) So that`s why it was marked wrong ?

[Dimitra956826]

Because when something doesn't sound as natural, it's best to be avoided.:P

There are probably more than a few ways to rephrase a sentence in Greek, and grammatically, all of them could be correct. However, we are not trying to teach every sentence structure that exists, let alone the most uncommon ones. Sometimes they sound fine, sometimes they just sound awkward. In other words, one could use some of them and get away with it in some cases (unfortunately, these cases are not something that can easily be explained. It's just a matter of what sounds best), but if they're talking or writing to a native speaker, uncommon structure is one of those things that will point out the fact that they're not a native. Sometimes, it's better to compromise with the best translation, than searching for ways to rephrase it, risking awkwardness in speech. :P