I woke the computer from sleep and Googled ‘jealousy’. Unsurprisingly, the internet was awash with information. I quickly found an article about something called ‘morbid jealousy’, which is also known as the Othello syndrome, a suitably dramatic label. Morbid jealousy, I read, is where a person is convinced their partner is being unfaithful despite having no proof. They are delusional and become obsessed with the notion, torturing themselves and their other half.

The more I read, the more worried I became. The articles and Wiki pages were stuffed full of terms like ‘psychological illness’, ‘mental disorder’, ‘insecure attachment’ and ‘extreme obsession’. There were endless news reports of people – mostly men, which gave me some reassurance – who had become violent and attacked their partner because of perceived infidelity. Othello, if I remembered correctly, murdered his wife, but most sufferers of morbid jealousy kill nothing more than their relationship.

I read on. Apparently, for women, jealousy is more likely to be triggered by emotional infidelity than by sexual betrayal. I thought about Charlie’s rant about what she believed I’d done with Sasha. It had been intently focused on sex. But maybe, really, the attack was caused by me offering Sasha emotional support, my closeness to her similar, in Charlie’s mind, to a romantic attachment.

Charlie had, I was sure, a psychological issue, probably with its roots in something that happened in her childhood. She was so sketchy when it came to talking about her past that it seemed logical that there was something hidden in her past that she didn’t want to face; a history that was causing her to be jealous now.

Pleased with myself for finding a rational explanation, I sat back.

We would find Charlie a counsellor, a therapist. Someone who could help her get to the root cause of her jealousy. Then, I assured myself, everything would be all right.

I made coffee for Charlie and took it in to her, gently shaking her awake.

Her eyes were wild for a second before she focused on me.

‘What time is it?’ she asked as if she had somewhere she urgently needed to be.

‘It’s three o’clock.’ I handed her the coffee. Sitting up, she took a sip, grimaced and put it on the bedside table. ‘Listen, Charlie, I’ve been thinking, about this morning.’

‘Oh God.’

‘I think that we should find you help. You know, like a counsellor or a therapist.’

She looked at me sharply. ‘I’m not crazy.’

I was aware that I was talking to her like I would a child who’d done something very naughty. I changed my tone. ‘I know you’re not. But jealousy . . . It must be rooted in some . . .’ I struggled to find the right words. ‘. . . self-esteem issue or insecurity.’

She groaned and pulled the quilt over her head.

Flummoxed, I said, ‘Charlie?’

‘Yes,’ she said eventually from beneath the quilt.

‘Will you please talk to me?’