Does it count as a breach of an oath if a shop is rented to the partner of the original tenant, knowing that the intention was not to rent it to the original tenant personally?

If you did not utter the oath, it is a laghw (idle/unintentional oath) and nothing is entailed by it. However, if you uttered it, then it is a binding oath. The majority of scholars hold that whoever swears an oath by divorce and then breaks it, his wife is divorced, whether he intended to effect the divorce or merely to threaten. As for Ibn Taymiyyah, he is of the view that a person who swears an oath by divorce for the purpose of threat is obligated to pay an expiation for an oath (kaffarat yameen) and his wife is not divorced.

The fatwa (definition) (religious ruling) adopted by us is that of the majority. Therefore, if you break your oath, your wife is divorced. Breaking the oath occurs by renting the shop to the aforementioned man. As for renting the shop to his partner, if you intended to prevent the utilization of the shop absolutely, then you would be breaking your oath by doing so. However, if you intended to refrain from renting the shop to him due to his bad treatment and did not intend to prevent its utilization absolutely, then you do not break your oath by renting it to his partner. The permissible oath is by Allah Almighty, whereas swearing by divorce is among the oaths of the wicked.