I understand the feeling. I want a little girl too, and if I have a boy, honestly....I might even cry. I've got a daughter who is 8, two boys who are 6 and 4, and than I've had a 14 week and 16 week loss in 2012 and they were both boys as well. I'm just ready for a fresh start emotionally and I'd love a girl. This is probably our last so if we had a girl we'd feel so complete.
As far as your son goes, he probably will be disappointed. My daughter is dead set against having another brother. LOL! She wants a little sister too push on the swings and do nails with and stuff like that. Alas, if she doesn't get a sister and your son doesn't get a brother they are young enough where they will adjust. Just like us, if we don't get genders we want we will painfully adjust too. LOL!
It will all fall in place. Baby will be apart of the love and loved regardless of the gender. I think it's just the worrisome and eagerness that make it hard during the pregnancy. Once they are here, in our arms, that will be it. I'm pretty sure you and I would still be a little disappointed, but it will melt away and kind of become a "eh...i guess i can't change it!" feeling. Once we hear it's first cry with it's first breath, nurse the baby, hear it's first coo, see it's first smile...than even that will probably just vanish and while we will always long for another child of that gender, the disappointment won't ever be that strong anymore. xxxxxx ((hugs))