When you love a cat or dog, two things are resolutely certain. He will fill the empty spaces in your heart with love, and someday he will break it.

If you’re not a pet person, go ahead and stop reading: This is a grief that’s alien to you. If you were raised on a farm, house pets might mean little more to you than furry livestock. If you’re consumed by human suffering, they may seem too trivial for your anguish. If you’re allergic — well, you may sniffle a little, but that’s just pet dander talking.

But if like Russ and me, your pets are an essential piece of the puzzle that makes life beautiful, and you’ve certainly shared the sorrow of laying a dear furry family member to rest. And you’ve grappled with the question — what next?

Do you honor your lost friend (and preclude future pain) by leaving his spot forever empty? Or do you fill the chasm with another fur friend who can never quite measure up to the memory?

And — not insignificantly — do you secretly seize this moment as the easy way out? Do you grieve your loss while silently ticking off the unspoken advantages … no more late-night walks at the end of a leash, no more latrine duty with the litter box?

Cats and dogs spin the circle of life far too fast. From adorable fluffball to slow-moving senior stretched out in the sun, from playful pup to white-muzzled elder who needs a boost to get into the car, they speed through the goofiness of youth to poignant old age in much too close to an instant.

We faced the inevitable when our talkative 9-year-old tabby, Miss Muffett (above), died. We were genuinely shocked. Cats are masters at hiding what hurts. We knew she’d been slowing down and were headed for the vet at the very moment her heart came to a dead stop.

It’s far from the first time we’ve lost a four-legged member of the household — just the first when we didn’t have a chance to say goodbye. Over the years, our three good dogs have lived out long and comfortable lives. All came to us as adult rescues, the last two from Adopt-a-Pet; all repaid us richly in laughter, love, wagging tails and enough loose hair to fill a mattress.

Our feline friends have, more or less, just appeared. The first became our studio cat when the young man who’d gallantly “rescued” him noticed he lived in a no-pets apartment. The second willfully chose us while our newly independent daughter was picking a pair for herself from a friend’s latest litter.

How many cats is too many cats? We’d figured the magic number was two. But when little Miss Muffett caught my eye on a kibble-and-litter run to PetSmart, we negotiated a new normal: Three. Three would be our limit, just this side of “crazy cat lady.”

Which is not to say the urge went away entirely. I “like” every kitty meme on Catbook — I mean, Facebook — watch every video, read every rescue story, share every cartoon. Only days before Muffett passed, I’d spotted a sad-faced black-and-white puss who’d been waiting at the Marshmallow Foundation in Detroit Lakes for nine long months. Now I understand the magic of online dating. One look in his sad golden eyes, and I was in love.

I showed Russ. We read about his trials and his timid disposition on the Marshmallow website. Then we reviewed why three cats were our limit, and …

… and then Cat No. 3 left the land of the living. Now what? Fate had clearly supplied the answer.

Welcome home, Mick.

But introducing a younger male cat to a couple of good old boys is not as simple as shaking hands and scattering a treat or two. Mick was our first experience with adopting a full-grown rescue — a 3- or 4-year-old who’d lived the hard-knocks life before the bedraggled, beat-up fellow was captured by a kind angel and delivered to the rescue group. Our second cat in particular, who claimed the household title of Top Cat when he was small enough to fit in a shirt pocket, had plenty of thoughts to share.

Nor did the extremely timid newcomer turn into a social butterfly when we unzipped the cat carrier and injected him into his new home. We started slowly, booking him into a private room in the basement. Even that small space seemed to overwhelm him after nine months spent in a 2-by-3-foot cage. He dived under the bed and stayed there for the better part of the next six days, venturing out only to nibble kitty crunch and do his business as the resident beasts sniffed suspiciously at the door.

When he’d worked up his courage to tolerate the occasional chin skritch and belly rub, we deemed him ready for his debut and left his door open. He greeted freedom with … nothing, not even a twitch his long, silky black whip of a tail. After lights-out, though, we heard the pitter-pat of the not-so-intrepid explorer padding up the stairs and down the hall, his toenails tentatively tapping along the wooden floor. Finally he stuck his nose into our bedroom and announced himself with the tiniest meow. When the incumbents rumbled out a few hisses and half-hearted yowls, he disappeared in the blink of an eye … but left a greeting of sorts in the upstairs litter box.

He’s been coming closer. We’re fascinated by Mick’s hesitant steps as he stretches out and settles in. When he found his way onto the screened porch, spotting sparrows and squirrels for the first time in nearly a year, it brought tears to my eyes. Then he fell asleep with the breeze in his face and the hot sun on his back.

That evening, we sat as still as mice as he sidled to a spot just inside the living room doorway. Clearly, TV was brand-new to him. He cautiously padded up to the Channel 6 newscast and froze, then reached out gently to touch the screen with one paw … just as our toddler granddaughter had done the first time she glimpsed “Peppa Pig.”

Just two weeks into our common life, Mick is blossoming — cautiously curious, sedately playful and blessed with plenty of shedding fur. He lingers just beyond arm’s reach, though he’s willing to accept a pat or two in passing. Peace with the homeboys? Still under negotiation. As for an unexpected leap to cuddle in a waiting lap, that’s merely a dream … for now.

No, this wary boy with a troubled past will never replace sweet Miss Muffett. Not even close — not yet. But he seems to be a perfect fit for the gap she left behind.