I thought I had told you many times.  But here for the record:
Because you are feminine yet strong.
Because you are extremely capable and can do things I know not how to do.
Because you are productive and extremely hardworking.
Because I can see how much you fight for the things you hold dear.
Because you can give others a lot of love and care (sometimes that was me!).
Because you have a gift for interior decorating.
Because you create a sense of home which for me appeals at a very sub-conscious and visceral level.
Because you're good with cars.
Because you love cats almost as much as I do.
Because you love a lot of the other things that I love; movies, wine, beer, fish and chips, sandalwood and more...
Because you opened my eyes (and ears) to new kinds of music.
Because you had the same PIN number.
Because you slept so soundly you couldn't be disturbed by my snoring.
Because you liked my thighs and didn't think my mouth was too small or "mean".
Because you made me two beautiful cushions, that are in colour schemes that show real artistic ability, and which I shall cherish till the end of my days.
Because you look vulnerable with your hair up in a chignon.
Because you are the first woman who ever helped me make marmalade or cookies.
Because you look cute in pigtails.
Because you pout your lips upwards when someone is taking your photo.
Because you study really hard to improve yourself, and achieve great marks through sheer will and determination.
Because I see qualities in you that you probably don't see in yourself.
There are probably many more, but it's 3.30 am.

Oh yes, one more:

Because I find you beautiful to look at.