This is just a stream of consciousness of Sherlock's. Rachel, his daughter would be 16 and Mason, his son, would be 13. At the moment this is just a one-shot, but I don't know if I should continue it into a fully developed story.
I truly loved your mother.
I understood the emotion. I had adapted to ensure she was in my life. Without her, I would not have you or your brother. Without her, I would not be the man I am today. I'm still anything but normal; normal is boring. But I had a complete soul and access to that which makes us all unique.
She loved you with all her heart. She loved you enough for both of us; just in case. I love you too, but I don't think you understand that. I don't think you know what it means to be loved. I don't think you know what it means to be excited, happy, sad or angry. You might feel them, but you don't show it.
The emotion you're feeling is pain. Or at least you should be. It's wretched and overwhelming, except you can't process it. You should be angry, you should hate me; but you don't. You're brother did; he's spent a lot of time with Aunt Sarah. Dealing with everything; he has your mother's emotional range and it's killing him. All he wants is his sister's logic and reassurance.
You had always put on a front Mon Cheri. You put it on for your mother because you didn't want her to know that you were more like me. More like me than even you could understand.
It was Christmas, many years ago, when I worked it out. You told your mother you still believed in Santa; at first I thought it was for the benefit of your brother, Mason. Upon further scrutiny, it was for her. You didn't want her to know; that you'd worked it out when you were three. Santa wasn't real! You weren't excited and you couldn't show your own joy; just a mirrored reflection of your mother's.
I took you to the coast on Boxing Day and you spoke to me like an equal; you would have made your Uncle Mycroft proud. I knew there and then that you were inflicted with my curse. I also knew that while you were hiding it from your mother; I could not do anything about it. You wore a mask to everyone but me.
Then your mother got ill. We didn't tell you or your brother but she was a ticking clock. It was at her request.
My biggest mistake and eternal regret; I'd ask for your forgiveness but you don't seem to care.
You'd spent time at boarding school by now. Not our wish, but yours. Mason followed your lead and joined you a year later. It broke your mother's heart but
I watched your mother fight. She began joining me on cases once more; something I didn't want but it gave her a new lease of life and I began to think she could get through it. I began to think she'd be ok. I watched her sleep while my mind buzzed.
She stepped in front of the gun aimed at me. I always wonder if that was always what she had in mind; to leave this world on her own terms.
She's been gone a year, and so have you!
Mason came home and is working hard at the local school; the one Uncle John went to. He has a girlfriend and supportive friends. He misses you. You missed his birthday; he'll forgive you though. If only you'd get in touch.
Rachel, my darling daughter; your mother didn't need you to tell her you loved her. You may not understand, but you did love her, in your own way, and she knew it. Rachel, she knew you were like me and she still thought you were perfect. She would not want you to live this life of isolation because you don't feel like you belong.
You belong to me Mon Cheri; please don't abandon me.