Difficult decision on the horizon

If you're a regular reader of my blog, you'll know that I have two dogs.  The older one, Spark, is beginning to age rapidly now.
I can see that sometime in the not too distant future, I might have to make a really difficult decision.
Spark's legs don't always do what he wants them to, he's going blind and deaf, and although I am doing my best, his skin is flaky and he's lost most of his thick downy coat, leaving the coarser coat.
Even writing this is upsetting me.  I need to talk to my children about him, and possibly need to talk with the vet.
Spark is the first ever dog I have had, and I didn't realise how much his visible aging would upset me.
I've been weeping on and off all day.
And yes, I'm putting off talking about him, so have been avoiding talking to people.