I was 44 years old when love finally found and changed me. It didn’t hover around gently either; it came from above and hit me like a cartoon anvil.

It was 2013. I was 30 kilograms overweight, drinking and smoking like a Russian soldier and resigned to being alone and lonely for the rest of my life.

It’s not as though I hadn’t had relationships. I’d been engaged – unofficially – in my 20s and nearly popped the question again in my 30s.

Either choice would have been diabolical, because both times I had to ask myself if I was doing the right thing. When true love arrived, it was so astonishingly pure, so simple, that time and space kind of stopped.

But while my heart was open to a workout, my body was another matter.

As my 30s slipped into 40s and friends had pledged hearts at altars and given me godchildren, my career path was disjointed and I had nobody to love or love me. I stopped exercising and took up screens and eating as serious hobbies.

Hard-living carelessness – falling asleep drunk on the couch after 18 stubbies every Friday and Saturday night, cordial and cashews stashed by the bed for midnight binges – saw me hit a desperately unhappy 115 kilograms.

At 115 kgs and ready for a life makeover.

The bachelor life was one of not answering to anyone, let alone the ghost of my past self, he of the effortless 32-inch waist. I couldn’t look anyone in the eye because of self-loathing, avoided social situations and didn’t care about anything. Then along came Kate.

Her brother had been a good school friend, and I had a crush on her at 14. She married someone else. I joined the navy at 17 to escape a clichéd but real-life evil stepfather. Decades went by. My parents died. Her marriage ended.

Then there she was on Facebook, commenting on a throwback photo of me as a teenage quartermaster gunner, all confidence and 1980s glorious hair. Her brother suggested we all meet for dinner.

One Saturday night later, we were immediately and irreversibly in love. Not wanting to commit to a walking heart attack, Kate – a tiny, disciplined fitness machine – issued concise instructions. One day to give up wearing jeans and runners. One month to give up cigarettes. One year to start moving.

I wanted her. The bad fashion and ciggies went. And eight months in I got on a treadmill.

I was like a human wax candle: the weight melted off. The endorphin rush, sense of reward for effort and having to buy smaller clothes every month was addictive.

Suddenly food wasn’t my only comfort and best friend, and being folded into a family meant salmon, steak and salad around a 7pm dinner table. Friday nights were toasted with just a vodka and soda or two.

With six gym visits a week, my waist dropped from 42 inches to 34.

Kicking back at 84 kgs, arguably the world’s happiest man.

Emotionally, the change was even more drastic. I’d developed a cynical, intolerant and self-centred armour to stop anyone getting close, but suddenly a woman and three children were smashing holes in it.

The kids – then 16, 18 and 20 – were all remarkable, all smart and all accepting of me when it would have been understandable for them to hit the reject button. It killed me.

I first met Sadie, the youngest, with her mum for pancakes. I was terrified but she was funny, warm and interested. If she was taken aback by my size, she didn’t let on, and her unexpected farewell hug nearly undid me.

The boys were more wary. But I knew what it feels like to see your mum with someone who’s not your dad. We circled each other for a while, but they got how much I adored Kate. The rest followed.

Being close to all three has made me a better man. I love them like they’re my own, but it’s not a synthetic emotion. I want them to be successful and happy, and want to be there for all of it.

Honey, I shrunk myself: in Italy in 2016.

It’s the stuff of greeting cards, but it’s funny how incredible life can be when the happiness of people you love becomes the main reason to live it. It’s such a sad thing that neither of my parents got to meet the person I was put on this earth to be with. I’d lop off 10 years of my life to give them, especially mum, just one day with her.

Within two years, I weighed 84 kilograms, got married, gained brilliant stepchildren, finished fun runs and took a beach holiday for the first time in decades because I wasn’t ashamed to take off my shirt. I’m not the same person mentally or physically that I was five years ago.

I’ll probably always feel I wasted precious years and wish Kate had fallen in love with me in 1984 – our kids would have been licensed superheroes and I’d be president of the world – but you can’t undo what’s done.

Love came late. But now I know what the fuss is about. It gives you the perfect reason to change.