I plonked my coffee cup on the table and turned to say something to my boyfriend, Jack.
But he was down on one knee.
We were in the middle of a busy cafe.
"But it's only our second date," I spluttered.
We'd met through a mutual friend and had both agreed it was love at first sight.
Now, on our second date, he was proposing already.
It was sudden but still I was unhesitant in my reply: "You're crazy, but yes!"
The next day he bought me a glittering diamond ring.
Our family and friends were absolutely dumbfounded.
"You hardly know each other," my mum protested.
"When you know, you know," I shot back.
After the proposal, we wasted no time and moved in together.
We were deliriously happy.
Then, three months later, I realised I was pregnant.
We were nervous but happy about it.
Jack was by my side when our son James was born.
He was an amazing dad.
When he wasn't at work at a coffee shop, I didn't have to lift a finger.
We were so happy.
Then one day he told me that his workmate Tom and his wife Lucy had invited us to their place for dinner.
"You'll like Lucy," Jack said.
Sure enough, she was a hoot.
She was warm and friendly and the two of us hit it off straight away.
"Jack proposed on our second date," I told her.
"Isn't that a bit quick?" she gasped.
"Yes, but I knew he was The One," I replied.
"Aw, that's a real love story," she squealed.
We became firm friends, popping round to each other's houses or going shopping together.
Then one night, Jack spent the evening at Tom and Lucy's.
I didn't mind, but the next morning he let something slip.
"Tom had a rubbish shift at work yesterday," he began, then stopped, realising he'd put his foot in it.
If Tom had been at work then that meant Jack and Lucy had spent the evening on their own together.
I decided not to say anything about it.
Lucy was my friend, and Jack and I were madly in love.
But after that I noticed that Jack and Lucy often exchanged flirty glances at each other.
"Is something going on between you two?" I asked Jack one evening after Lucy had left.
But a few nights later, Lucy and I were having a couple of glasses of wine and she confessed she'd like to kiss Jack.
"I just want to see what it's like," she said.
Then one evening she called, upset. "Can I come over?" she asked, sobbing.
She and Tom had had a fight.
"We're going through a rough time," she said.
My heart went out to her.
"Of course you can," I said. "Come over now."
Soon after, she was on my doorstep red-eyed and tearful.
Jack and I settled her down on the sofa with a glass of wine, then Jack made himself scarce.
"It'll calm down by tomorrow," I told her. "I know how much Tom loves you."
Later, Jack returned saying he'd messaged Tom to tell him that Lucy was at our place.
Soon Lucy was laughing and smiling again.
"Why don't we watch a film," Jack suggested.
Our TV was in our room so we all snuggled up together in our king-sized bed.
Jack was in the middle, with me and Lucy on either side of him.
We settled down to watch Me Before You.
It was a sweet film, but I'd been up early with James and was shattered.
After a few minutes, I felt my eyelids start to droop.
Soon, I was snoozing.
Waking up, the room was dark.
Drowsily, I realised the bed was moving.
There were suspicious groaning noises too.
Suddenly I was wide awake.
I realised my friend and my fiancé were at it in the bed beside me.
In a state of shock, I hesitated, unsure of what I should do.
Should I wait and see what happened?
But I couldn't lie there and listen to their romping, so I sprang to my feet.
"What the hell are you doing?" I screamed at them.
They sprang apart.
Jack was stark naked and Lucy still had her top on but frantically yanked up her knickers.
"Get out!" I raged.
Lucy grabbed her things and fled, while Jack scrambled around trying to put his jeans back on.
I went into the kitchen and collapsed to the floor in a sobbing heap.
I couldn't believe what had just occurred in my own bed, inches from where I was sleeping.
It was the ultimate betrayal.
Jack finally showed his face and started pleading with me.
"It was a romantic film, we'd been drinking. It will never happen again," he said. "Sorry, Katie."
But it wasn't enough.
They'd been so brazen about it, and our baby boy was in the next bedroom.
"I don't ever want to see your face again," I yelled.
He stuffed a few of his belongings into a bag and skulked out.
I messaged Tom and told him what had happened.
I caught them shagging in my bed, I texted.
As well as feeling hurt, I also felt like such a fool.
My family had been right after all – I'd jumped in at the deep end with Jack and got swept up in the whirlwind of our romance before really knowing what he was actually like.
The next day, Lucy texted to say that she and Jack had slept together a few times before that night.
In a way, I was glad the truth was out – and that it happened before I married that slimy toad instead of after.
But I still had a rough time getting over the whole thing. I had to force myself to see him, for James's sake.
In time, I slowly got over it.
It's been a year now and I'm feeling much stronger.
I've found a new man who treats me right and I'm also expecting again.
I still can't believe what happened between Lucy and Jack.
Men usually meet their mistresses in secret behind closed doors, not cheat in the same sheets as their partners!
Jack confirmed with Take 5 that he'd slept with Lucy in the same bed as Katie.
*Lucy and Tom are false names.
WATCH: Cheating husband is confronted by his wife on camera.