Is it normal that i still think about...

Quite a few years ago I was on holiday with my family and had to share a room with my sister. We'd never been particularly close growing up, and argued more than anything else - she's 2 years younger.

One day she was in the bathroom and I was in the bedroom area and she shouted for me to bring her drink into the bathroom, to my surprise she was in the bath, sat up so I got a perfect view of her (not inconsiderable) boobs. Every day after that she asked me to bring her drink in for her, and she also started being a lot less modest with getting changed etc

An evening near the end of the holiday she was lying naked face down on her bed and for some reason I joined her and ended up lying on top of her, she said nothing as my now very hard cock nestled between her butt cheeks, we stayed like that for a while then I got up - there was pre-cum all over her ass and thighs.

She said nothing about it the next day, but nothing more ever happened. I still think about it now and wonder if I should have gone further and whether she really wanted me to or just wanted the attention (she's always been an attention seeker).