Some times boys are so stupid and it makes me mad!!

So I am ashammed (srsly I have never in my adult life been ashammed of my family) to say that my little brother has been cheating on his girlfriend for a while now I haven't talked to him just his girlfriend and shes pissed I would be to. So mad in fact that she threatned to never let him see his daughter again. I think I'm really mad at her for that but alas I'm really mad at my brother but I don't want to be. We have never really gotten in to a fight........... but srsly you can't keep it in your pants? and come to find out it seems like I'm the only one who didn't know. I guess my little brothers dad and stepmom new and even like this slut girl, and my sister knew or at least that is what gf is saying. I guess the sister thing kinda makes since because she would be the one he would tell ( I get mad and she doesn't) so he would go to her and ask or talk about it.
Even better yet slut girl is married and from what I've been told (don't know how true it is) LB (little brother) has been having daughter call new GF "mommy" I am so mad about this (alas I don't know if its true or not) how could you do that to someone. and ps the mom is a really good mom. and how bout this for a thought maybe I need to step back and not really do or say anything I mean really is it my place to say anything? ( although I'd like to rip him a new asshole) I just want to be in this little girls life and want her to know me and want to love her. In the end tbh this girl is to good for my brother, and slut girl, (wife) of the other guy and my little brother ....well lets just say that they deserve each other......

P.S. I know I'm missing caps, and commas and all sorts of good stuff ... sorry I just had to get it off my chest. Thanks