I've been with Lily the whippet for under a minute and she's quivering like she's shitting blades. It smells like Wotsits and rotting meat. The turd is so pungent that, despite being eight to ten metres away, it smells like Lily has defecated over my shoes. "She's on the lamb," says owner Ali, by way of explanation. This isn't a euphemism for something else, like dog periods; Lily is literally just being fed a lot of lamb.

A bit like having a baby! I offer. "I don't want to be the one to say that," she says, "but I did have a friend who said, 'You've had it harder with your puppy than we had with our baby.'"

Ali and her girlfriend are both in their early thirties and currently live in north London – a move they planned around Lily, the dog they were going to buy together. It was only there they'd have the necessary space for her: Hampstead Heath, where I've joined them on their morning walk. Everything about their life revolves around the dog: nights out (or lack of), freelance working schedules, exercise. Ali tells me: "I was looking at Instagram the other day and noticed I barely posted in 2017, and was like, 'What were we doing in 2017?' It's because we had a puppy: we literally didn't go out. You just end up talking about dogs all the time."

Dogs have always been called Man's Best Friend, but I'd argue they've levelled up a notch as of late. Until recently, people didn't communicate almost exclusively in silly dog videos. Until recently, dogs didn't have their own social media accounts and get booked for meet-and-greets . It is evident times have changed.

As a generation, millennials are infatuated with dogs. In fairness, most people like dogs, but we've taken our love and made it part of our generational identity. We squeal and coo when we see them led around. We've ramped up their rom-com use as dating bait (instant right-swipe). We are hypochondriacs but let them share our ice-cream. There aren't enough names for the doggos, doggies, puppers and Good Boys that we love so much.

As Bob, 35, and Molly, 29, who own Billie, the chihuahua pug, put it: "She costs nothing, sleeps through the night, and our single friends still want to hang out with us." For someone single, sociable, career-minded and renting who can't imagine their life five years ahead, let alone owning a house and having a baby, it's an achievable dream. Something to grow up for.

A recent study found that 44 percent of millennials see their pets as "practice" for babies, given the fact this generation is getting married and having children later in life than the generations before them. Increasingly, they're not just practice, but an alternative to children. This is perhaps a city-centric observation, but none of my friends in their late twenties talk openly about hopes of having a baby; rather, we flinch when we see a child walking around, out in public, on its hind legs. It's a fluffy friend we want. One that'll love us, not drain our minimum finances and not get in the way too much.

That was the motivation of Ali, who says, "It was more about the lifestyle, if that doesn't sound too tacky; of being outside more and having companionship during the day."

"In your twenties and thirties, you want to feel responsible for something, but you don't want to have a family. We still feel very, very young," says Julian Victoria, editor of DOG, a chic lifestyle magazine for dog owners. DOG's readership are of millennial age and mostly independent artists, creatives or freelancers. "When you see a bunch of mothers sitting around having coffees with babies in prams, that's the same as with dog-owners," Julian continues. "You end up going to the same places, to the park, you meet others walking dogs. It's a community that a lot of young people are realising they want to be a part of."

Kait shows me a photo of a tiny grey and white puppy called Isla, who she's going to pick up in a month. "I would never be able to get [a dog] if I didn’t know how well set up London is for doggy daycare, and borrowers, and people who just want to look after dogs, as I don't think it'll impact my career or life, or ability to go back into a full time career," she says.

"I have a lot of queer couples whose dogs are literally their children," she says. "There are a lot of single #singledogdads and #singledogmums. I can't stress enough how much their life revolves around their dog! Very, very few of my millennial clients have children."

Twenty-four-year-old Kait runs Doggy Day Care, a London-based dog care service, and says most of her clients are successful people in their twenties and early-thirties, a mix of both cishet and LGBTQ singles and couples.

It's obviously relevant, too, that millennials are the freelance generation. Businesses get it; WeWork-type office spaces allow dogs to sit alongside humans where they can, and some offices even offer a dog-walker. A poll recently went around the VICE UK office about allowing employees to bring dogs to work, and when a rumour spread that one member of staff had been seen clicking "no", many publicly seethed with rage.

Significantly, many of the dogs Kait looks after have their own Instagram profiles. For some dog-owners, a dog is simply a part of their personal brand. Why produce a baby who only you find charming when you could have a gorgeous Chow Chow who will rake in the likes? Be the graphic designer with the Shih Tzu, the app developer with the German Shepherd, the businesswoman with the English Bulldog. Your pet can even be an extension of your beliefs and social causes (I'm a big fan of @mildredthesausage , who is owned by a female couple and recently wore a rainbow cape during Pride month).

A key element of Kait's service is that she provides clients with endearing updates; she starts WhatsApp chats for every dog, which she updates with five photos and messages throughout the day. Her Instagram is an adorable checkerboard of dogs, something else the dog owners love. She says this account alone has brought in a number of clients.

A dog is also something to be directly monetised if you so desire. These dog Instagrams – go down the rabbit-hole and find endless accounts with tens of thousands of followers – are earners, all Lily's Kitchen brand code discounts and Pets At Home-sponsored posts.

Ignoring the way we make every aspect of our lives into work, dogs are great content. Julian at DOG says something that sticks with me: "Whatever dog you have is a symbol of your personality. As human beings we are fans of making that statement – we are attracted to a breed because it aligns with our personality." It's why we send a cute chihuahua slobbering everywhere to our best mate on WhatsApp with the caption "me when you save me leftovers", or feel like we'd be just that bit closer to ourselves if only we had a long-haired Yorkshire Terrier with a bow.

And when we can't escape the post-ironic way in which we view the world, or let go of the earnest anger we feel towards the news cycle, dogs do the trick. "There's something in them that triggers people to become more soft, more sensitive," says Julian.

It's during this new age of loneliness in which we've learnt that the love and bonding hormone, oxytocin, is sparked in both dog and owner when they look at each other. A generation reporting high rates of anxiety and depression is well aware that caring for animals contributes to a lower blood pressure and rates of stress. "It's a boost to have someone run around the house shouting with excitement just because you came home after work. Unconditional love feels great," say Bob and Molly of Billie. "She's hilarious and brings you out of yourself when you're down in the dumps, just by sneezing and looking confused, or something like that. She's a real serotonin boost, I've no doubt."

"They're so, so much work, but I can see why people want dogs," Ali had said when I explained the premise of our meeting. "You have to stick to your little routine. There's something really steadying about having a dog. It's lovely, actually."