Don is out of boyband - presumably he took to the bottle? (4)
I believe the answer is:
baby
'don is out of boyband presumably he took to the bottle?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he took to the bottle?' is the wordplay.
I cannot really see how this works, but
'he' could be 'ab' and 'ab' is found in the answer.
The remaining letters 'by' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for baby that I've seen before include "Timid person; child" , "New-born child" , "Infant" , "Very small (version)" , "Honey" .)