I'm very sorry to hear of your budgie's untimely passing...
When budgies first start to show signs of illness, it's always best to have them seen by an avian vet specialist, so that they are properly examined, diagnosed and given the right treatment plan that will get them back to full health.
This is the standard procedure to be followed when a person has a pet.
When ignoring signs of illness and the ongoing deterioration on the pet's health, this very sad outcome is to be expected.
At this point it's not possible to determine the exact causes which led to your Zweedle's passing. We can only assume he passed away from an ailment that had been bothering him for the duration of at least one month.
Be sure to give extra TLC to your female budgie. If you take the time in reading the vast information on general budgie care here at Talk Budgies, you will be in a better position of providing the very best of care to your female budgie in terms of taking into account her overall health and happiness.
I'm wishing you and your remaining budgie all the best in this very difficult time.
Rest in peace little Zweedle.