Thinking of a brovelove fic lowkey based on the song Good Luck, Babe! where during one of Simon and Agatha's breakups, Agatha and Niamh start something, but Agatha's still trying to make herself fit into the roll of Simon's happily ever after/dealing with internalized homophobia, so she's unsure and keeps their relationship secret. It hurts Niamh and when Simon asks Agatha to get back together (maybe get married after school?) Agatha takes him back, telling Niamh it's just the way it has to be.

Then years later they're middle-aged, Agatha stuck in a loveless marriage/in the midst of divorce with Simon, and Niamh lonely, she's dated other women but they just didn't work out. And they reconnect somehow, not exactly willingly (maybe smth do to with politics at Watford, or related to Mr. Wellbelove's clinic?) and they kinda hate each other at first, but also miss each other, and it's messy but eventually I think they'd work things out and start again.