It was fun at the time and I still look back on it that way.
This is totally innapropriate for her sister to be doing.
But, what you need to do is head right now to your local police station and file a report.
First man up, good job you got a bj from your sister's friend.
Touching the head of the dick stimulates all of its 4k nerves so it's no surprise you came lol.
And you need to do something about it, or they'll think its okay to do.
My sister-in-law was staying over.