For their fourth date, Caleb asked her to his dorm common room to watch a movie. Now, in St Mary’s speak, ‘watch a movie’ definitely has a dirty connotation. I’ve gone to at least five different common rooms to watch Baby Driver, and I didn’t even know there was a car in it until the fourth time. So, after Mary Kate left on Friday night, I wondered, Should I have given her the sex talk?

Nah. I mean, this is Mary Kate we’re talking about. Girlfriend got her sexual awakening from that kid in The Secret Garden who can talk to birds. So I figured my room-mate was safe with Caleb and his Jesus Sandals.

And I was quickly reassured when she walked in five minutes before curfew, smiley and glowy, but with her school shirt still buttoned up to the top.

‘So what movie did you guys watch?’ I asked her, pulling out my earphones and sitting up in the bottom bunk. I’d shoved all my dirty clothes into my army duffel, but never actually got around to doing laundry, so I was using it as a backrest.

Mary Kate sighed happily as she slipped off her loafers. ‘American Experience: The Pilgrims.’

I wrinkled my nose. ‘That educational thing about the uptight people with the big buckles and smallpox?’

Mary Kate sighed happily again, watching her own glowing face in the mirror as she took off her cardigan and folded it lovingly over her arm. ‘Yes.’

Okay. Nothing to worry about.

Then, one Sunday night, Mary Kate arrived late to dorm mass with big news.

Mass had already started. All the St Theresa Hall girls were gathered in our dorm chapel in sweatpants and pajamas, the opening chords were sounding on the chapel piano, and the overzealous freshman choir member who was always too intense about banging her tambourine was banging her tambourine. The incense was burning and Father Dan was about to make his entrance. I looked around, frowning. Mary Kate wasn’t going to miss mass, was she? She never missed mass! Especially not with Father Dan – he was the Bieber priest!

Tambourine Girl had already pounded and rattled her way through a full verse when Mary Kate scurried into the chapel, flushed, her hair loose and rippling. She crossed herself rapidly with holy water, grabbed a hymnal and slipped into the crowd beside me.

‘Where were you?’ I hissed.

‘I was with Caleb,’ Mary Kate whispered. ‘And guess what? He’s asked me to walk around the lake with him!’

This was what Mary Kate had been waiting for. This was like Elizabeth Bennet and Mr Darcy finally exchanging that chaste peck on the lips after six agonizing episodes of letter writing and blue balls in tight trousers. Only Mary Kate hadn’t been forced to wait that long – she had practically achieved her semester goal already, and it was only September.