My best friend is with an older boy

I don’t know what to do about it She’s going to turn 15 next year and I guess that makes it okay? Her boyfriend is 18 and he makes me feel weird. I asked her mom and she said it’s fine because he was 17 when they met and something about Juliet laws? I googled and I guess it counts? Google says 3 to 4 years is okay but I don’t know it’s weird He’s touchy and he also flirts with me with her right there Whenever I talked to her she called me jealous. I don’t know what to do

So. Help please