My cat has recently gone of his food and water, he also doesn't want any treats. He has recently lost a mate. He is still a bit active, still purring and meowing. He hasn't been sick at all.
Any ideas on what could be wrong with him?

If your cat is not eating or drinking you need to get it to the vet. He could get dehydrated and die as a result. Not eating for a few days will not kill him but not drinking will.

Tish, how long is "recently"? If it is just a day, this behavior could go hand in hand with your cat grieving for his "mate." Animals do grieve. Bushg is right, your cat can live without food but he needs to drink his water. If he refuses to drink or eat anything for more than a couple of days, you need to give your vet a call and make an appointment for an exam as soon as possible.

Hi all, great news, I took my cat to the vets, it turned out he had a infection in his belly, she gave him some antibiotica, and as soon as we got home he went straight to his food and water, thanks for your help :) :D

So glad to hear that kitty is OK! Good for you for taking him to the vet right away!

I am happy to hear that you took her to the vet and it was something easily treatable. Thanks for giving us an update. Often we are just left wondering what happened. :)