To add on to this, there is a very sharp divide between solo traveling to get yourself out of a rut, or because you're fed up at work and want to rethink your career objectives, or because you want some time to yourself following a breakup etc - and solo traveling to fix much deeper mental health problems/deep rooted personal unhappiness.

If you fit into the former camp solo travel can be great. If you are part of the latter camp solo travel almost certainly will not help you. You have to brutally honest with yourself before embarking on long-term solo as to exactly why you want to travel, and if you decide that the answer to that is "because I'm deeply unhappy and have been for a long time" then professional help will always be your best choice.