Sophie, hun, whilst I think your story refers to you realising your 'secret project' is going to be too much work so you're sacking it off, there's actually something far deeper it also applies to.
The thing you truly 'thought you wanted but no longer do' is motherhood. Unfortunately it is NOT okay to 'change your mind' and you cannot 'start over' because Barney is not a dog and you cannot rehome him. You can run away from your degree, you can run away from YouTube, you can run away from your 'secret project', heck, you can even run away from Dave, but Barney?! He's forever sweetheart and he deserves so much more than what you give.