since she left? Maybe he is pinning a bit for her... dogs can do that...

Have you established that he isn't ill? Best way to check is get the meatest bone you can find, or even use some hamburger or frankfurters... see if you can coax him to eat that... I think it would be a good deal to just have him checked out at a vet just in case.. then if the vet gives the all clear try the following...

Extra attention is good... If you are a dog person, which I assume you are or she wouldn't have left him with you, then get down to his level and talk to him and have lots of physical contact... don't talk to him in a low tone.. rather make it upbeat and fun... does he have a favourite toy? through the toy around while in an excited mood... calling and talking to him all the while...

Use the food suggestion above too... Chicken breasts with rice and some natural stock is also a good "treat"

I have gone on line to see if I can find anything else for you to try, but all they suggest is natural herbal remedies, which I don't think is very neccessary unless you talk to the vet about it.

Hope this helps a bit:-)