Wow, you're really trying to get back into some semblance of normalcy. If you worked all you could on that project, it makes no sense to start thinking you did badly on it. If you did your best, that's all you could do. That's honorable enough, even if you couldn't get to where you really wanted to be. Getting back into things takes time, even if you're trying to go about changing in full force. Don't be concerned. You have to ease yourself into change, and you can't be too hard on yourself.
Things haven't been easy for you at all, but the greatest thing you can do for yourself is believe in your ability to recover. Take it slow. If you're still hit by setback after setback, don't sweat it. It's not your time, but in the future you'll be hit with a great success if you stick to it now.
As for your recent assignment, I'd just say to buckle down and try to get it done. The motivation isn't there, but you'll feel a lot better about yourself if you can get it done. At least do a bit of it. If you fail, you can try again. There are always opportunities. You'll always have an opportunity to live better, so you've got to get through these rough spots. Focus on getting the project done. It doesn't matter if you do it half-halfheartedly or grudgingly, or even if you're putting all you have into it. Just get it done.
Hang in there! We all doubt whether it's good to be here. Sometimes it feels like it would be better to have a permanent ticket out. But that would be such a waste. You have so much human potential in you and it would be a waste to die with all that you can do never being born. Try to see yourself through this tough time. I'm positive things will be looking up for you soon.