I'm in much the same position. Last year I lost 15kgs and put almost all of it back on over the Summer break. I understand what you mean about the fear of 'failing' again, that's the reason I put off restarting my weight-loss.
The best advice I can give you is don't see slip ups, no matter how big or small, as failing, see them as learning curves. You've got to make mistakes to learn how to combat them in the future.
The thing about the gym is understandable too. I've been joining gyms on and off for the last four years, always thinking I'll get to a point where I enjoy it. However, the truth is, the gym isn't for all of us.But that doesn't mean you can't get a sweat on. Find something you like doing, be it walking, swimming, playing any sport imaginable or simply dancing around the house while nobodies home
And remember, there will always be support and understanding here.