Very brave of you! It's hard; I know. When I put my Beardie, George, down in 2016, I was devastated! He was 11 and I'd had him almost that long!
It wasn't until a year later that I was ready, and willing, to get another bigger lizard. That's how I ended up with Frank, my Blue Tongue Skink. He's got great personality and we love him.
However, it's really hard when you lose an animal. You want to mourn and pay respect to them, but as a keeper/parent, want to move on at some point too.
I know it was really hard with Bonsai, because you did everything right, and it didn't work out. At least with George, it was his time, and he had a good and long life.
I am really happy you got another snake though. You seem like an awesome keeper/parent and I have no doubt that Neptune is going to have a great life!
I am sure Bonsai is looking down happy as well. He knows you honored him and did the best for him. He will always be in your heart.
Keep chugging buddy!