Hey folks,
I wrote a story! It's called "Mine!" and it's available to buy in a collection of stories called Stealing Muscle. The anthology is put together by JGmuscle12 (https://www.deviantart.com/jgmuscle12), who is also the author of one of the stories, and all proceeds go to some great classic charities, so that's fun. All the stories in the collection have the theme of stealing muscle in one way or another; in "Mine!" a statuesque and unhappy physique competitor and kickboxer steals her fiancée's new muscle growth powder and discovers some long-hidden truths about herself and her relationship. There's a bit of light violence and domination in it, and some pretty hot sex.