
I agree that the fact your boy is picking on a puppy may be because he is under the weather and the pup is aggravating him around the sore area. Even a male Mal tends to accept puppies.
As far as his "friend" goes, it sounds like the honeymoon's over. I have two Mals who loved each other and were the best of friends until earlier this year - and now they are apart permanently :( The youngest was about the same age as yours, and he just decided it was time to test who was Boss!
I assume by your comment about being grumpy and not wanting to come in, that he has started to question your right to tell him what to do! Some Mals do, some don't, but you need to remain firm and consistent at all times. You could find that castration will calm him if he's a dominant male, but if you aren't sure, take him along for a Tardac injection (a sort of chemical castration) and this will give some indication whether castrating him would ease your problems.