The level of pessimism here seems a bit gratuitous. Working with my partner worked well for me, but I've seen people in similar situations achieve a lot of succ

The level of pessimism here seems a bit gratuitous. Working with my partner worked well for me, but I've seen people in similar situations achieve a lot of success through participating in supportive online communities (e.g. a Slack group for alumni of a coding bootcamp), or coworking with friends (whether or not everybody is working on the same stuff). Therapy can also be helpful, both in addressing the roots of the problem and in providing some external accountability. And there are doubtless many other options if you look around a little.