If an individual lives alone and suffers from anxiety/depression could he listen to music in the 9 days?

Shalom, Thank you for your question. The question of listening to recorded music during the three weeks, and especially the Nine Days (at the start of the month of Av) as a sign of mourning, has been addressed by many of the Rabbis in the last generations. While listening to music is not one of the major forms of mourning, such as eating meat or dinking wine, haircuts and weddings, none the less, the practice amongst Jews for hundreds of years (if not more) has been to refrain from playing and listening to live music. With the creation of recorded music in modern times the Rabbinic opinion has been divided. Some forbid all recorded music, even if it is pure vocal singing; others allow slow or sad music; some allow only vocal acapella music. Beyond all this – in the case of depression or anxiety, we should compare these cases to other situations of ill-health. For example, it is forbidden to eat meat during this time, but someone who needs meat for health reasons is allowed to eat it (they should preferably eat chicken before red meat). And so too, bathing for pleasure is forbidden – but washing for health reasons is certainly allowed. This being so, in the case you ask about, where a person needs to listen to music so as to maintain good mental health, it is permitted. Preferably this should be coupled with the lenient opinions about what music is permitted – that is, rather than listen to happy dance music, if listening to vocal music, or soothing classical music would suffice, that would be best. Blessings.