Friend dating a minor- what do I do

One of my friends is going on 21, and she is currently dating a 16 year old. In my state age of consent is 16, but under 18 is still considered a minor. Statutory rape is also defined as sexual interactions with a minor. I’m pretty confused here, is what she’s doing illegal? Or is it just more so gross? We’ve been out of high school for 3 years now and he’s a sophomore. The whole thing freaks me out.

Am I a bad friend for not wanting to be friends with her because of this?

(Id like a note that a 5 year age difference doesn’t bother me when the both parties are over 18-20 at least) (I am also aware her relationship is one of my business but it does raise legal questions for me, just concerned for her sake if either side of parents found out)