Dog Days

So, for the last two days I've been dog-sitting my roommate's dog, Shadow. Shadow is a black Australian Shepherd. He's four years old, smart as a whip and sweet as pie.
A couple of days ago, he tore a pad on his left hind paw and he's finally quit limping on it. So, tonight I took him outdoors for some gentle play. I threw the ball a few times and Shadow happily trotted off to retrieve it. I didn't do nearly as much as we would have normally and I spaced out the play over a couple of hours. But I've noticed he's still favoring that paw, and I'm not sure what's going on with it.
In addition, he's been a bit down in the dumps since his 'dad' is gone. Shadow knows when Jorg isn't around and he sleeps a lot more which makes me wonder if he's suffering from some kind of canine depression. When Jorg returns tomorrow night, this dog is going to fucking explode with excitement/joy.
I don't mind looking after Shadow. I've known him his whole life and I guess if Jorg's the 'dad' then I'm either the 'uncle' or the 'mom.' I'm the one he hides behind when he thinks he's in trouble. I'm the one he comes to for comfort.
It's a nice feeling.
Now if I could just convince him not to wiggle around in the bed so much....