Alec put his key into the door slowly, his hands shaking violently as he turned the key. This was too familiar. He remembered the first time he'd come to this very door. Now this would be the last time, he thought bitterly.
Turning the handle, he stepped inside and climbed the stairs, dreading the task ahead of him. On reaching the apartment, his legs nearly gave way beneath him. Everything was as he remembered it. Same coffee mugs lying on the table, same smell of Magnus in the air.
After what felt an age of standing at the edge of the apartment holding onto the wall for support, he took a deep breath and began the slow task of gathering up his things.
Eventually, Alec was forced to go into the bedroom. He'd left it until last on purpose. He nearly collapsed when he walked into the room, seeing the unmade bed and clothes littered all over Magnus' side of the room.
Trailing his bin bag behind him, Alec grabbed his things, barely even looking at them as he threw them into his bag.
When he had finished, he took one last look at the room, then turned and headed for the door. As he was about to leave the room, something caught his eye from the wall beside Magnus' side of the bed. It was a photo of them in Italy: Alec frowning wearily, as a bemused Magnus wrapped a sparkling head band around his mop of black hair. Catching his breath, Alec ripped the photo from the wall, and added it to the top of his pile. Magnus probably wouldn't even notice it was gone, he thought bitterly as he headed into the main room again.
Sitting down on the sofa, he clasped his head in his hands and began to sob, letting the events of the day catch up on him fully. He knew Magnus wouldn't be back for hours, and he didn't want to leave the apartment just yet. A few hours were all he had left. Then we would have to leave his key and walk away from the home he thought he would always have.
After sitting on the sofa for what felt like hours, but must have been only about ten minutes, he went and got a notepad and pen from Magnus' desk and stared thoughtfully at it.
He had resigned himself to the fact that he couldn't go back to the institute. He wouldn't be able to handle the pitying stares and questions. Not for a long time. Maybe not ever. If he went away, it also meant that he would never see Magnus again. He knew that this was what Magnus wanted, but he couldn't bear to leave without leaving some kind of message or apology for Magnus.
Lifting the pen to the paper, he began to write:

[I] Magnus, I know what I did is unforgivable. I wish I could explain why I even considered doing that to you. Why I kept going back to Camille. But I can't. I'm so sorry. You won't see me again. I know that's what you said you wanted. But, it- [/i]

Alec stopped for a minute, trying to stem his tears enough to finish his note. His last farewell.

[I] But it still hurts me. Leaving you. And, I wanted you to know that I understand. I finally think I understand. You were my first and only love. But you've lived a long time, and you've loved a lot of people. I understand now why I love you so much more than you love me. Well, loved me.
I know I'm just trivial to you, one lover in a long line of them, but it kills me on the inside that I hurt you. I wish there were words bigger then these I could use to describe how I feel. I'm sorry. I love you, Magnus. [/i]

Alec

Alec frowned. The note was still legible through his tears. Only a few small parts might not be readable.
He set it on the desk, about to leave, then sighed and threw it in the small waste bin in their bedroom. The note wasn't even worth leaving.
Standing up, he took one last look at the place he had called his home for the last few months, then set his key on the table and walked out the door.