Only you know if you can truly go back. All I can offer is this; when my job (I was a lawyer, and a damn good one) got to the point where I felt like I was giving up who I was and compromising my principles, I eventually made the choice to go. It wasn't easy and there were several factors that went into it, but at the end of the day, my mental health was worth more than the paycheque.

As far as the point of it all, I too am an atheist, and to me, the point is love and kindness. You give animals, as you would people you love, all the love, support and kindness you can until their, or our, time is up. Honestly, it's little comfort when one of ours dies, isn't it? The hurt, the hole is there and there's no fairy tale to fill it or give it meaning. There's just fucking loss. What keeps me going is before that loss, there was love. You gave those animals, those wedding table ones, a wonderful life. Ad the ones you cared for professionally, well, you gave them the best you could.

There's no shame in walking away. There's no shame in going back. There's only you and what's best for your health.