Is swearing by other than the name of Allah, such as "by love," "by friendship," or "by passion," permissible in Islam?

Firstly: It is forbidden to swear by other than Allah and His names and attributes, and this is a minor shirk. If the one swearing believes that what he is swearing by is of the same status as Allah or greater, then it is a major shirk that expels one from the fold of Islam. Therefore, saying "I swear by friendship" or "I swear by love" and similar phrases are forbidden.

Secondly: Saying "in the name of love" or "in the name of the homeland" and similar phrases have details: 1. If the intention is to seek blessings (tabarruk) and assistance (isti'ana), it is shirk, which could be major depending on the status of what one is seeking blessings from. 2. If the intention is to express as a proxy or representative of a group, then it is permissible. 3. If the speech is about abstract matters like love and loyalty to enhance the discourse, it is not shirk, but the speaker is sinful if the speech is obscene, or about forbidden relationships, or with a non-mahram woman. If it is between spouses, it is permissible provided it is private. 4. If the speech is about noble meanings like brotherhood and loyalty, it is permissible provided it conforms to Islamic Law (Sharia).

Thirdly: It is forbidden to establish relationships between non-mahram men and women in any field, whether personal or through calls or correspondence, due to the spread of indecency and incitement to sins therein.