Ok so my headcanon for why Mary and Damien are so close (i.e. my special boy) is that they’ve known eachother forever - I’m talking since school/university, and they’ve always been best friends. Even when they both got married they made sure to call eachother almost every day and find time for “girls’ nights out.” But then a little while after Lucien was born Damien came to the full realisation that he was trans, and that he couldn’t live any longer without being his true self.
Somehow, while he was terrified to tell anyone, the idea of telling Mary made him the most anxious - even though she already accepted his growing gothic wardrobe, and his overwhelming love of dogs and graveyards. But he was scared that once he told her they would never be the same again, since he wouldn’t be her ‘best girlfriend’ anymore.
He waited, and waited, trying to find the right moment, to pluck up the courage. But if he couldn’t steel himself enough to watch Nightmare Before Christmas, then how the hell was he supposed to do this. Nevertheless, one day - when he’d lost count of how many times he’d gone into the basement to cry after hearing Lucien call him Mom, and he’d received yet another text from his best friend saying 'heeyyy *deadname* how are ya?’ - he went to her house to tell her.
She was quiet while he revealed everything, anxiously mentioning anything that seemed relevant to lessen the weight of the silence between them. He talked about how he felt as a child, and when Lucien was born; his nausea when wearing dresses and how much he’d cried recently; his ideas for a new name. And then, because of course they had to surface right now, his anxieties about what it would mean - how much he loved her, but how scared he was that he couldn’t be her best friend anymore.
When he’d finally stumbled to a halt - and she had that look on her face that meant she’d just been waiting for him to shut up - she said: 'No, you’re not my best girlfriend anymore. You’re my special boy.’ And she hugged him, so he burst into tears on her shoulder. From that moment on, she’d used that nickname to signify that she wasn’t fucking around when it came to their friendship (usually when Joseph got frustrated about how much time she spent with another man.)
She then helped him to come out to his husband, and to Lucien - and she sounded like she’d read fifty guides on how to come out to children, even though Damien thought she never read anything without romance or spies somewhere along the way. And a few days later, a package arrived at his door which turned out to be a Victorian-era appropriate binder - which he had no idea could exist. The invoice inside read Joseph Christiansen, but there was a note from Mary:
'Apparently these things are a bitch to get on and off. Let me know if ya get stuck and need rescuing, special boy. M xx’
And he knew things with Mary could never change.