by Dar_Jisbo
When I was in high school [mumble] years ago, one of my best friends was "Harry" in this story. I've changed the names and enough details so people can't figure out who he and the sisters are unless they already know. [Yes, "Harry" and "Nell" are still together: their two kids are now young adults.]
What a nice story! I would have given the more mature Harry some hair on that muscular chest, and given both of them a bit more in terms of description of their bodies. A good reading.
This type of thing happens quite often. It just develops from familiarity to something more.
If only all men not only cared for their GF little sister, but came to love her like he did...