Pippo is a perfect example of taking everything so seriously and not letting anything go. He would celebrate like crazy any goal even in a seemingly meaningless game, which in itself is a reason why he has won so many fans' hearts. He is upset nowadays as he is no longer in Allegri's plan, to me it is totally understandable.
There isn't much Allegri can do though, after all, Pippo is not in his plan. Yes, some complains that Pippo should not be given just 3 minutes out of every 5 games, instead, he should be given 15-20 minutes per game as he 'deserves more respect', but we all should know that if he gave Pippo 15-20 minutes every game, Pippo still wouldn't be happy - he would want more, ... and more. If Pippo is not in his plan (he is not), what Allegri should've done is being brutally honest (my guess is that he was being honest - don't know about the part if he was brutal enough) and having him move to another team (my guess once again, is that maybe Allegri had made himself clear enough, but B&G were cheap enough and let Pippo stay).
I feel bad about the current situation, but it is for the benefit of the team. Allegri certainly has done nothing wrong, as he should have the best interest of the entire team put as his top priority; and he is. I would take the side of Allegri, if side-taking had to happen. But I honestly wouldn't blame Pippo either - his attitude is exactly what drove him to much success and made him a legend and you can't honestly expect him to change overnight.
The longer this relationship goes on, the more painful. I actually hoped that what happened to Albertini happened to Pippo also. It was painful but it was quick and both parties accepted and moved on quickly. I think Pippo should move on and continue his legacy elsewhere. I have no doubt that he still has much to contribute, but sadly, it will not be with Milan.
Grazie Pippo, and Forza Milan.