She is about 6 years younger than my DW and very good looking indeed, but has never really had a serious boyfriend and I think she is a tad jealous of her sister (DW and I are hand in glove).
I would NEVER do anything, but I can't help fantasising about her. She once injured her knee and DW suggested I massage it - with DW in the room - I obliged but when my SIL asked me to move my hand in a Northerly direction to massage her quads, I felt a bit hot under the collar TBH and broke off.
This is not an "am I normal" or "am I being unreasonable" thread, because (a) I know it's normal, and (b) it won't be unreasonable unless (to quote J.L. Picard) I make it so.
Just wanted to share...