I'm 24 years old and have full custody of my 16-year-old sister. She has been living with me for the last 3 years. I found out today, from her, that she has been lying to me about spending time with a female friend in order to spend time with her new boyfriend. She confessed this to me because she would like for me to have dinner with them both tonight so that I can meet him. During this, she has also told me that he is 18 and will be a senior at her school this year.
Some good points about this: she told me herself, she has immediately asked me to meet him, and she has offered me his parents' phone number if I wanted to contact them.
Some bad points: she lied to me about where she was and who she was spending her time with (this specifically violates a house rule regarding her car and keeping me informed of her whereabouts) and a 2-year age difference, as he will be a legal adult in our state next year.
In our state, he will be a legal adult at 19 and she will still be a minor. 2 years in your 20's is nothing, but I feel that 2 years in your teens is a major difference in emotional intelligence and responsibility.
I have agreed to the dinner with them both, and I am compiling some questions and rules to address. But I'm really struggling with how I should go about punishing her previous actions, if I should even punish her at all? It is obviously not okay to lie to me, but she has been very mature in our communication today about this all.
Update after the dinner last night: I didn't go into it with the view of needing to interview him for the position, but instead took the time to get to know him. What his interests are, what his favorite class is, if he had any plans for the future. He's not a bad kid, and definitely not the boogy-man that I was expecting when I heard he was a big bad 18-year-old. I get the impression that my sister was expecting me to grill him, and she seemed very relieved after the first few minutes of this casual conversation. As for why she decided to lie to me she said something along the line of, "I was expecting you to be upset with me for seeing someone, and the longer I waited to tell you the harder it got to bring it up." After which she apologized and seemed to breath a little easier. I have shared this post with her today, and I'm hoping that using the answers provided here we can both work together to foster a more trusting environment. Thank you everyone, I appreciate you all so much!