Replying to Broski's dirty deeds

there's probably two ways you can walk away from this. either cheering on the little man or hating on him.
i just want to get an opnion on this story.

last night i went tomy friends grad/bday party with my family in tow. this includes my mom and my 16 yr old brother, with his new girlfriend who turned 15 about a week ago. i call her skipper because she looks like barbies sister of the same name.
after skipper left my friends and i, along with some younger kids were talking about what a manwhore my brother is. he's had countless gfs within the last year and hey let's be shallow, they're nothing to brag about. he broke up with his gf of two years earlier in the year because " she was annoying" which turned out to be 16-yr-old for she didn't put out. last night his friend told me, in confidence, that my brother had lost his virginity to skipper recently, oddly enough while he was still dating a different girl.

all in all i dont approve because of the cheating aspect, and also because it was on the couch in our basement. it's no biggie that he's 'becoming a man' but i don't even think he has the balls to go buy condoms if need be.
--at this point i'm wondering if i should ruin the newfoudn bond with his friend and confront him, just so i can give him the "talk" about being safe.. and NOT FUCKING ON MY COUCH, but i also don't want to mess up my new snitch. if he told me this, id hope hed keep me updated with whatever comes along.
my brother hasn't told me himself but he's not being too slick about keeping it a secret. he has an obvious couch-burn from the subpar fabric on our couch, and also displays some scratches on his back as he wanders aroudn shirtless.

so, am i overreacting? and should i confront him or just let it go? thankss