You did a wonderful tribute to the life of your very precious girl, Moon.
And I can relate perfectly to the feelings you're having. I have had budgies since I was 5 years old, I literally grew up with them, watched them very closely and learned the facts of life with them. The love my first pair had, their eggs and chicks, I felt so blessed to be witnessing all and with them I also learnt to love and respect mother nature.
Even though your Moon is not present in physical form, the memory of her lives on in your heart and through all the happy moments you shared with her.
I hope both you and Sun will feel better as time goes on. Maybe one day he will find another mate, it's certainly not impossible, I can tell you that from experience.