Why: I think I can sum this up with a quote from the Manga.
Miroku: To me, you are, a special girl. However... that is precisely why, I can't
love you as a girl. You are a companion to fight along-side with. That's how I feel.
Sango: I, I know that...without you having to tell me. It's not like I thought
that... you did love me...
Sango: That's enough of this conversation, right. I'm going.
Miroku: This conversation isn't over yet. If, when the battle with Naraku
is over... the curse of my Air Rip is broken, and I'm alive... at that time, would you...live with me and bear my
Sango: I...I will...
Miroku: You'll bear them!?10, or even 20?
What more needs to be said. He cares alot about her and she him. They just belong together. I totally reccomend
reading this in the manga. It's volume 30. For a link check out the links page.