Did a revocable divorce (ṭalāq rajʿī) occur and an expiation (kaffārah) become obligatory for someone who swore to change residence within two months but did not do so until after a year?

If the husband says, "Upon me is an oath (عليّ اليمين)," reference is made to his intention: did he intend divorce or an oath by Allah? If he had no specific intention, then reference is made to the common usage of the term. Since you did not change the apartment within two months, having forgotten your oath, the most probable ruling is that no breach of oath (ḥinth) occurred, and neither divorce nor an expiation for an oath is binding upon you. This is because, in most opinions, abandoning something in an oath due to forgetfulness or coercion is not considered a breach of oath.