Just replying to the OP here.
Moti if your dh is basically saying to your second son that he loves him in spite of him being a boy, then what will he say to a third or fourth boy?
The problem here is not wanting a baby girl, the problem is your dh and his attitude. If you did have a girl now, do you not think that your second son would be pushed out? He's the boy they 'love' in spite of him being a boy, very much in the middle with an older brother who was the first boy and a younger sister who was the coveted girl.
It is attitudes like your dh's that screw children up for life. It would not be fair on your second ds if you were to have a girl now, knowing how your dh already speaks to your ds.
Why tell your ds something like that? Most parents just tell their kids they love them, there are no 'buts' or 'in spite ofs'. The very fact that your dh felt the need to tell your ds that says a lot about him.
I think he needs to get over his obsession and you should not be trying for another baby given his current state of mind and appauling attitude. If you really want a girl, as someone else said, there is always adoption. In fact there is a huge shortage of adoptive and foster parents. That's an awful lot of little girls looking for adoptive families but not finding any.
As for selective gender IVF. Morally I could not have healthy foetuses destroyed purely because they were the wrong sex.
But the main reason you should not have a girl is because of the way your dh treats your second ds now which should ring huge alarm bells about the way he would be treated (i.e. ignored) if you were to produce a girl. Your duty is towards your children first and foremost and as a mother you should not be putting their needs and priorities on the backbench in favour of your husband's selfish wants. If he can't love his son without adding in buts then he's not fit to father any more.