I'm very sorry to hear of the events leading to your Sugar's passing...
You have my deepest sympathies.
Breeding budgies or any other living being under our care is a very serious task. Before going through the breeding route a person needs to have a very good knowledge of the species, to be able to understand and decipher their behaviours, the ways they communicate, to look at them and be able to tell if they are in good shape health wise or not and to do a whole lot of research in order to have all the bases covered before first attempting breeding and be more prepared in case something does go wrong during the process and provide immediate assistance to the breeding pair and/or the chicks when needed.
Breeding is a big responsibility and leaving things to chance is not the way to go. Close monitoring is essential.
Again I am very sorry, this was a really hard lesson that you had to learn and I hope as you start to heal, the grief and guilt will go away.
Rest in peace, little Sugar.
You can take this time to give some extra attention to your budgie Spice and work on bonding more closely with him. Watch his behaviour as this will give you clues as to how he is coping with the loss of his mate. If you notice he is getting depressed, has lower energy and hardly sings, then you can get him a friend. You don't need to get him a female. Male budgies can bond very well and be happy as best buddies.
If you do choose to rehome your Spice, make sure he goes to a good home.