Is removing your hijab in front of a person who has promised to marry you – after your vow to Allah not to remove it except in front of your husband – considered haraam and does it necessitate expiation?

If a woman's intention is that no non-mahram men see her, then the suitor seeing her does not break her vow, because it is permissible. However, if her intention is that no man sees her except her husband, then the suitor seeing her obligates her to offer expiation, because he is not yet her husband. And a covenant with Allah is considered a vow, and its expiation is like the expiation for an oath.