Summary: I loved him, and Sometimes He loved me too.
After a lifetime together Alec fades away more and more each day as he forgets Magnus.
Alec has Alzheimer's.
Today was turning out to be a rather dismal day, Magnus thought to himself as he let himself out of the bedroom, leaving Alec alone, perhaps later it would be better but such had yet to happen lately.
Magnus sighed as he made his usual coffee and texted Izzy and Jace about what they were dealing with today. Then Magnus sat in his chair and rested his head in his hands. It broke Magnus' heart to see Alec like this, it hurt more than the days when Alec forgot who he was mid-sentence.
Today was a day where Alec had no clue who he was, on days like this he usually came up with a lie for him, such as he had been severly injured on a mission which had required a Warlock's healing touch, and then he'd summon Izzy or Jace to come be with Alec.
Alec had been losing his memories for decades now, some days even Jace was not known to him, once they had been only on occasion but those days were becoming more frequent as Alec's mind faded further and further, even magic could not bring his memories back.
Catarina and Magnus had spent close to three years researching and creating, trying to find some way to fix Alec's mind but ultamatly they had failed and Alec had asked Magnus to stop, told him that it hurt to see Magnus' hope fade more and more after each failed spell.
And so, here they were, Alec's mind fading more each day, untikl one day Alec wouldn't remember anything about Magnus, until one day his body forgot how to keep breathing and he died.
Magnus had always thought that it was worst to have his love taken from his suddenly, to be left behind when said lover realized that Magnus was different than they were, that he would stay forever as he was, but he realized that watching Alec slowly fade from who he had loved and who had loved him was far more painful and soulbreaking because Alec was losing his memories of them, of all they had been through and it broke Magnus' heart to see his strong Shadowhunter revert to that scared young man he had first met.
When Alec had first begun to forget Magnus had taken to reminding him of those little things, thinking nothing much of it, until one day twenty years after they had become lovers Alec had forgotten that Magnus was his husband.
That day had begun as any other, Magnus had woken to the sight of his husband still sleeping in their bed. And Alec's eyes had slowly blinked awake and had thrown himself from the bed in a panic screaming and asking who he was and why was he in Alec's bed.
It had taken some time to explain, and Jace and Izzy agreeing with Magnus for Alec to believe Magnus and the lost and terrified look that Alec had had that morning as he sat in their kitchen with his favorite coffee cup, the one that said 'My lover is Magical', was one Magnus could never erase from his own memory.
After that day Magnus had taken to reminding Alec of everything important, that they were married, that Alec was Head of the Institute, that the Clave was headed by Lydia who had bee making it more acceptible for Shadowhunters to love who they would as long as they were happy.
Until one day even that no longer matter, Alec no longer remembered him and panicked at the sight of him waking in their bed every morning, so Magnus had et himself up in the guest room and waved away Izzy and Jace's well-meaning but unnecessary offers to take Alec to Idris or Alicante. Instead Magnus had reminded them that he had promised Alec to love him in sickness and health and just because there was no cure for his sickness did not mean that Magnus was going to leave, not this time, not Alec.
Now, Magnus lied to Alec almost everyday and lived for those days when Alec would crawl into his bed and ask him why he hadn't come to their bed. And Magnus cried because one day, probably not far in the future Alec would do so for tha last time and Magnus would never again feel his lover's arms wrapped around him or his kiss to his cheek.
Izzy let herself in and Magnus dried his eyes and forced a smile for her as she nodded to him and went to talk with Alec.
One might think it woud be a relief for Magnus when Alec finally joined the Angel, but Magnus would rather have a memoryless Alec than no Alec at all.
As Magnus had said the day he married Alec, he was with Alec for life, in sickness ad health, Magnus only wished they had had more years in health.
Izzy came out and smiled sadly at Magnus, "He's sleeping now. It took him a while to recognize me."
Magnus nodded, it had been taking longer and longer for Alec to recognise even Jace and Izzy, Magnus thought it may have something to do with the fact that they were now in their seventies.
"I'm sorry, Magnus." Izzy said as she always did.
"I know." Magnus always returned, "I should start lunch."
"I have to get back, Jace is in Idris with Clary and their daughter so I had to leave Simon in charge."
Magnus walked her out and wandered back in to the kitchen.
"Hello, Magnus." Alec said softly as he stepped into the kitchen.
"Good afternoon, Alexander." Magnus smiled as he set lunch on the table, "How are you feeling today?"
Magnus had take to saying very similar things everyday, hoping to inspire, if not memory, then familiarity.
"Like I've been forgetting our life together." Alex told him as he sat down.
Magnus paused in his actions, "Are..."
"I remember us, Magnus. I'm sorry I keep forgetting." Alec whispered as he stared at Magnus sadly.
Magnus knelt in front of Alec and took his face in Magnus' hands, "Darling, it's not your fault."
"You dan't have to stay." Alec offered.
"No, I don't suppose I do, you wouldn't remember regardless, but Alexander, I choose to stay, I promised you in sickness and in health until death doth part us, I'm going to be here until your end, it was my plan to stay with you until that time came, and that is never going to change."
"And if I never remember again?" Alec asked as he looked at Magnus.
"I'll still be here for you, Alexander, when I said until death does part us it was not your death I waas referring to but mine." Magnus explained, "Until my last breath, my love, I will love you and be here for you, nothing, not memory, not age, or anything else will ever change that."
Alec pressed a small kiss to Magnus' lips, "I miss you when I don't remember who you are." Alec whispered softly, "It feels like there is something missing."
"Oh, darling, you never have to miss me, I'm right here."
Magnus drew Alec into a gentle hug.
Moments later Alec stiffened.
"Why are you hugging me?" Alec asked as Magnus released him quickly.
Magnus forced a smiled for his now suspicious Shadowhunter, "I needed a hug and you gave me one."
Alec narrowed his eyes at the Warlock but finally nodded.
"Now, are you hungry?" Magnus asked, "We were having a lovely lunch moments ago."
"Oh, I have to get back to the Institute..."
"Surely you can spare some time to eat?" Magnus offered.
Alec still hesitated, "I guess so."
Magnus smiled, "Thank you, Alexander."
"How do you know my name?"
"I know your family." Magnus told him.
"Oh."
Magnus wasn't aware of it at the time but it would be the last time Alec ever remembered him, though he never acted afraid of him again, simply accepting the Warlock that took care of him until one day the Warlock was no longer needed and the Warlock disappeared and no one ever saw him again.
I don't know what exactly happened to Magnus after Alec died but I'm going to say that he probably kept searching for a way to fix what Alec had and maybe when he discovers it he'll show back up.