Bone Cancer In Dogs

Here is whats happening.

-Female in heat
-Male wants her so he hasn’t eaten for almost 3 weeks
-They’ve been kept seperated since she was in heat

She is no longer bleeding but we aren’t taking the chance to let
them be together, we just tried to let them be together to see if he
would still try and mount her, and he did try. So, we’re still keeping them seperated until further notice.

I’m worried about the male because he hasn’t eaten since she’s been
in heat. All he does is sniff around the backyard like a freaking bloodhound. He barks and jumps on the door because he knows
she is in the wash room (wash room leads to backyard).

We’ve tried giving him gravy over his food, meat bones, and other doggy snacks but he won’t eat. His ribs, spine, and hip bones are showing and whatever we try and feed him he won’t eat.

The female is no longer bleeding, but he still tried to mount her.
We were supposed to get the female spayed 2 months ago
but my grandmother
was diagnosed with cancer, so we had to set it aside for a bit because we’re taking care of her because of two surgeries.

Is there anything we can do to make him stop all the whining
and get him to eat? It seems even if we try and feed him a full
piece of chicken from dinner he won’t even eat that.
The male is a doberman, so he is naturally lean, but I noticed
he started to lose weight when the female went into heat. I don’t
know what to do!!!
The doberman is my g-pa’s dog, and for some insane reason he REFUSES to get the male fixed. I tried convincing him but its always a steady no. I’m not asking who to get fixed, but rather how to get him to eat. Because after the female is thoroughly done being in heat, we’re getting her spayed.
The bacon grease is a good idea, we usually do that when the dogs don’t want to eat.
But we have no bacon!!!!