<human>: Can you give me a shortened version of the text?

This is, for obvious reasons, a throwaway.

Two of my close friends and I recently found out that our other friend has been having an inappropriate relationship with a teacher (she is 16, he is early 40s and married with kids). We are in high school. I knew something was up, so I badgered her until she told me everything. They have been seeing each other for about a week now, and they've done sexual things. She really has feelings for him, but I know that he's using her for sex. Not only is this illegal, but I feel like it's morally wrong for him to take advantage of a girl who, quite frankly, has very low self esteem. Also, from the way he acts around female students, I have a feeling this isn't the first time he's done this with a teenage girl, and if I don't do anything, I doubt it will be the last. I know that it seems obvious that the right thing to do is to tell an administrator, but doing this would (I think) mean that the whole school would find out about the relationship, and I honestly don't know if she could handle that.
I'm in a pickle here, any advice would be deeply appreciated.
<bot>: My 16 year old friend is having sex with a 40-something year old teacher, who is married with kids. I'm not sure what to do.