It's his private life, but man he is in his mid 30s, how can you be such a mess?
I think it's a problem that he is a captain, because clearly his performance hasn't been affected by his private life that much, but that is not the case for other players (Stones is a good example that when his private life was not good, his level dropped a lot).
As a captain the message to young players is: you can be a leader, have a messy private life and still perform, BUT that is normally not the case.
If there is absolute proof that the performance of our players would not decrease no matter what, then sure Walker can be a captain and do whatever the hell he wants.