A woman admitted to sleeping with a friend of 10 years – who already had a wife.

In an open letter admitting her wrongdoings, she said the sexual tension had been building for a decade.

And after plenty of flirting, she bedded her mate “B” who had been married for 18 months.

In a first person piece for MamaMia, the writer confessed she’d only been interested in her pal when he became unavailable.

She said: “There were a million ups and downs between B and I, over our 10 years of friendship.

“I didn’t want him when he wanted me, but as soon as he stopped giving me attention, I’d find some way to get it back – just because I could.”

A woman spoke about romping with a married man she'd fancied for years

She added: “I don’t remember the exact moment I found out about you, but I’m sure I was in a relationship and only started to care as soon as I was single again.

“He and I would catch up for drinks on the odd occasion... and what would start innocently would always end up with us making out like two teenagers who didn’t care where we were, or who was watching.

“You actually once messaged me on Facebook asking if he was saying inappropriate things to me.

“He was. But I told you he wasn’t, and that lie came so easily.”

The fling fizzled for a few years as the writer pursued a different relationship.

The pair reconnected online – and agreed to meet up

But when she was newly single, she decided to find out what her ex “B” was up to.

After a quick Facebook search, she discovered her former flame was married.

And feeling a “pang of jealousy”, she decided to send him a message.

This led to more flirting and “comments that a married man should not make”.

The pair slipped back into old habits – and decided to meet up for a drink.

The writer slept with the married man after sexual tension built up for a decade

At the end of the night, the writer smooched the married man and they took their relationship to the next level.

She admitted: “I turned to say goodbye, he grabbed my face and kissed me.

“He told me he'd had feelings for me for 10 years. Would it surprise you to know up until this point we’d never slept together?

“That changed that night. I knew it was wrong, but with 10 years of foreplay, it was honestly one of the best sexual experiences I’ve ever had.

“It was tender, intimate and romantic – but also passionate and hot. How could something so wrong feel so right?”

After cheating on his wife, the married man rushed back home to her.

His decade-long mistress admits she’s “still jealous” of their relationship.

Even though she says she’s “sorry”, she has no plans to tell the unsuspecting woman about the one night stand.

She added: “I often wonder which is worse - the deception or the knowing?”