Sick budgie with tumor, what would you do?

I always say this. It is the quality of the life not the quantity. If Chester is still to a point where he enjoys his life and is not in pain then I would leave well enough alone. He will let you know when it is time. I would say if he shows signs of pain, stops eating and singing all together and sits fluffed up then it would be time in my eyes. You must feel right with the decision you make for your beloved pet. You want no regrets. I have had to make this decision many times with birds, dog, cats and some I have made bad choices with and regret. I kept the animal around for me and not for them. My best advice would be if he is still enjoying life let him be the minute you see otherwise it is time to let your little friend go. So sorry I know how hard it is. make sure you enjoy the time you have with him as much as possible and cherish the memories. when it is time mourn him but celebrate his life as well. Also read the Rainbow Bridge Poem as I think it is wonderful.