Billu:
These are normal things that all relationships deal with -- the "spark" in any relationship, doesn't matter whether with Pakistanis or US or Indian or martian, that "spark" is something that one has to continuously keep alive - I mean it doesn't just keep burning on it's own - that's just the way it is and don't beat yourself up over it, - trust me, ups and downs in a relationship have nothing to do with the nationality of a person.
Now if I'm not mistaken, I don't think you have any problem with US girls, rather it's your parents, and in particular your mother, who has the problem -
I got that whole, "I respect and value my parents" - Duh - nobody hates and despises their parents -- but in the end, what makes you Happy? We all learn to overcome, for the most part, disappointments and we all grow -- your parents won't grow but they will overcome what they think was a disappointment, so long as you are happy -- See, your mother is really looking out for you - she doesn't want you totbe hurt, she want you to be happy --- but she also may be wrong about a whole bunch of things.
Peoples past -- Listen friend, you wanted somebody who was also a friend - trust me, you may not know that between men and women, that's a precious commodity, it takes a lot of maturity and compassion - remember peoples past, is just that, past -- but of course in Pakistani culture of Honor and shame, the past is always a issue, not the future or the present, but the past, kinda explains why we are stuck in the kinds of issues we are stuck in.
But, hey, your life - for whatever it's worth - don't beat yourself up over anything -- and everybody, please trust this, everybody has to fight for happiness, or they end up doing things that make them happy but they have to hide it from themselves and the world - not where you want to be.
Smile, it will work itself out.