It is not enough to show that the US petitioner will suffer or become depressed if their spouse is not allowed to return to the US. You will have to show that this depression would be severe....by having a doctor's evaluation...and letter. It would also be very persuasive if the couple has been apart before and the US petitioner has suffered depression to get affidavits from people stating such... Also, a doctor's letter speaking to this would be of great help. Obviously, if the US petitioner has an illness for which he/she is being treated here in the US...and leaving the US would be detrimental to her health.
US petitioner has responsibilities in the US and they can't leave
The US petitioner has kids here in the US from another marriage that would make it impossible for the US petitioner to leave the US. Also, if the US petitioner is caring for a sick relative and such relative would suffer if the US petitioner were to leave. Another argument that could be made is the US petitioner is heavily involved in her community and that type of work is truly important to the petitioner...and parting from such would be detrimental to the US petitioner.
oppressing conditions in beneficiary's country
The US citizen could argue (if true) that they could not move to Beneficiary's home country because there are oppressing conditions in that country for the US Petitioner (ex. a country where a female is discriminated upon or where a female would have a difficult time carrying out her career (for example), a country where religious worship is forbidden or limited to the detriment of the US petitioner).