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The issue here isn't culture or language or heritage; not at all, because as people here can attest (as can I), those things can be overcome if a couple is united and willing and strong enough to press forward. This man is not. In fact, families with combined cultures can be very beautiful, loving and healthy. That doesn't seem to be where this is headed.
It's very clear that culture is only an excuse. The fact that he has lived with you for so long without mentioning marriage AND kept you from the important people in his life (regardless of their feelings) means that he doesn't want to take this relationship anywhere, which means he most likely doesn't want to get married. This reality is heartbreaking and doesn't mean there's anything inherently wrong with you, except that you have tolerated it for so long. At the very least, you deserve someone who can say to his parents and everyone else, "This is the woman I love, I hope you love her; because I do."
My belief is that if his parents were not the way they are, then there would be another issue ie., "I'm not sure if I want to give up having kids" or "I just don't feel ready" or "My father is sick" or "Let's wait until the wind changes" or any number of other reasons men use to live with women for long periods of time without marrying them. There must be some other indications of this in his personality. Has he permanently committed to anything, like buying a house? Has he been married before? Does he freak out if you want to go to a wedding together? etc., etc., etc...
It's sad that he is shifting the blame here, but it just seems to me that his parents' cultural bias is a convenient way for him to avoid being totally honest. The fact you have characterized him as "cowardly" and "infantile" suggests that you already know this. I'm so sorry.