Really I have not found any better example of healthy and...dare I say pure S&M play anywhere for any kind of relationship. Gay, straight, younger, older, this series just outlines exactly why this isn't just some weird fetish people force upon themselves.
Have you tried reading Sunstone? its on DeviantArt look for the author shiniez.deviantart.com
its a really nice SM yuri... although it has a lot of the sex stuff haha (the author is awesome, the story pulls you in, and thats coming from someone who doesn't even like this kind of story..)
Anyway..I am kinda cheering for yuuka, but I know she just wont be able to change the SM fetiche..lol