Oh no! I totally understand what your feeling though. Just know that a lot of us here think it's super amazing! I've been eagerly awaiting more!
I'm studying to be a teacher and a lot of my classes are about the importance of books like this! There are a lot of discussions in class about how much books like yours mean to not only the kids but also the adults. We also talk about how so many children's books are valuable for and should be taught in older grades. Your book made me think of that! I was like "wow, this is definitely one of those all ages books! My teacher and artist friends are gonna love this!" And I honestly want to buy a copy when you publish it, even though I only speak and read in English and Spanish.
I hope you keep going! Depression and loss of motivation are hard to get through, I go through it all the time sometimes it helps to work on something else for a while and then come back to the work later when I feel a little better or re-motivated. Also taking some time then going back and re-reading/looking at everything that I've done can re-inspire me too!