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I'm with those who are expecting this will end badly. Having seen variations of culture clashing before (my grandfather was Chinese, grandmother Japanese--NOBODY from either family went to the wedding or started speaking to them until they had kids--in fact I think my grandmother's brothers were threatening physical harm--and that's just one example), yes, there is a culture clash here, and generally, there are two ways to deal with it--go with the family even if it makes you unhappy, or go against the family, even if it means they are upset with you/disown you etc. I wouldn't make a value judgement as to which way is better, but it's not as if either path is pre-ordained by culture or temperment. Each individual has to make up their own mind as each situation arises, and the evidence seems to point toward the BF taking the former path.
IF the situation is to work, though, the LW will have to make sure that her relationship with her BF is strong and that he is willing to acknowledge that his relationship with her is worth getting into a fight with his parents. And maybe he has been avoiding that possibility because it's too painful and it's more comfortable for him in limbo now. If he isn't willing to do that, it's better to know now than be uncomfortable a while longer.
And while some traditionalists take this sort of thing to the grave, there are many many examples of disappointed parents who later become pragmatists, realize they are only hurting themselves by holding onto a dream that is no longer real. People can come around, if given enough time. It's not just Asian parents--one can imagine it happening with some parents of gay children for example--or someone who really really wanted a child to follow a certain career path that the child didn't want.
And in my family, after the initial taboo was broken, everyone started marrying pretty much whomever they wanted, to the point where the family tree is melting into something quite different from where it started. Most extreme point--one of my uncles married a white woman and adopted her daughters (white also) from a previous marriage. One of my white cousins then married a man who is half Japanese, half black, but we have other combinations too.