First, I want to say I completely understand!!! My brother and his gf had a baby girl over a month before I had my DS2. I found out they were having a girl the same day I found out we were having another boy- needless to say I was hysterical. But, like you, I took comfort in the fact that my DS1 was so beautiful and perfect and my DS2 would be too- and he is!!! :-) The thing is, my niece is beautiful too- really beautiful. My situation differs a bit in that my SIL has a DS from a previous marriage and really spoils him, so it's not like she doesn't like boys. But I know that she is so happy to have a pigeon pair and that gets to me. All the really girly pics of her and my niece get to me sometimes, even though I do love my niece very much!
But my niece is not "perfect". For a while she was a very fussy baby, while my DS2 has been quite the opposite. I'm not a big fan of the style of clothes my SIL dresses her in, even though just the fact she gets to buy girly clothes at all makes me a bit jealous at times. My niece looks nothing like my kids (mine are biracial), and that helps a lot because I still feel like my kids have a very unique look, kwim? So I don't look at her and think that is what MY DD would like, etc. It also helps that my mom favors boys somewhat. While most everyone else I know seems to favor girls, my mom REALLY wanted me to have another boy and was thrilled when we did have a boy. She is extremely close with my boys (prob also b/c she watches them almost everyday). I too was worried my boys would be overlooked but it's actually been just the opposite! In fact, my mom calls DS2 her "baby" lol. I too wanted to have the first granddaughter, but I am happy I got to have the first grandchild. My DS1 is the only one who ever got to meet my dad (my dad passed away when DS1 was 18 months old). So while that is really sad, there is a specialness there too. YOU got to have the first grandchild, and that to me is more special than anything!
My in-laws are another story. I know if DH's sis ever has a baby girl the boys (including her own son, my nephew) will be overlooked big time. Even if I have a girl I worry, because I don't want any of the boys to be pushed aside. My MIL totally favors girls, I've posted about it many times on here. :(
As time goes on I have to say though, I am getting less and less jealous of my SIL. Her kids are 8 years apart in age, and different genders. While one time I wanted the pigeon pair BAD, I don't think it is my ideal anymore. Having two boys close in age in just amazing, knowing that they'll grow up real close just like my sister and I did when we were kids (she is 3 years younger). I already see the bond developing between them and it's so cool. Not that my SIL's DD and DS can't be close- her DS adores his sister. But there is a huge age gap. Even my SIL said to me some months ago that I am very lucky my kids are close in age and said she wished hers were too. I would LOVE to have BBGG, even better would be if I had twin girls next (I can dream right?) lol. So if I ever start comparing I tell myself how much cooler would BBGG be than BG, you know? Of course who knows if I will ever have a DD but that thought brightens my day. :)
So my friend, who knows? We could both end up having girls next, we never what life has in store for us. Just look at all the siggies on here of women who never thought they would ever have their DG and did. :)