It sounds like it has something to do with your missing budgie, since he didn't act this way before. Maybe he feels you are the reason his mate is gone and he doesn't want you doing anything to him. He will probably sing and chirp to try to lure his mate or another female budgie to him. Also, sometimes budgies will bite if they are in pain--did he hurt himself on anything?

My male budgie, has been acting really strange since this morning.. He has been biting the hell out of my fingers when I put my finger near him.. then next minute he's chirping, acting really happy and talking to me, then biting into me again! He's bitten so hard he's lifted the skin off my fingers.. I used to have another budgie, she was a female, but she unfortunately got out of the cage and flew away about 5 days or so ago.. Do you think it has something to do with the other bird being gone? He's never acted this way before..