I want to present a different viewpoint to that of Rafael, though I do expect that you would be at too much risk if you don't sever your connection with your boyfriend. But what's been left out of this interchange between you and rafael is CULTURE. I don't know if you're a Euroamerican or Chinese, British, or what, and what your boyfriend's background and culture is. If he comes from a country where prostitution is an accepted outlet for men, it would be expected that one lies about it to protect the relationship one really wants.
There are still some vicious backstories that aren't explained by a potentially prostitution-friendly background (I know a 30 yr old Australian former student who thinks it's fine to go to the legal brothels in Australia, and of course not tell his Japanese live-in girlfriend about it. I don't like his morals, but I'm an American, and I'm not willing to diagnose his personality because I'm not his therapist.)
One man's normal masculine prowess may be another man's personality disorder. But re Personality Disorder: It's only a PD if the person won't work on himself to change his behavior, and in your BF's culture there may be "nothing wrong" with the behavior that has shocked and sickened you--as it would me as well. It IS QUITE POSSIBLE that within a culture that's permissive of prostitution and hidden male cheatingt (and male cheating is quietly occurring in at least 80% of cultures world-wide, tho resisted by men in modern times in some) your BF has developed very dysfunctional sexual habits due to psychological issues in childhood and adolescence--but that's still not a personality disorder, unless he is unwilling to take on the challenge of changing his attitudes and behavior to fit with the expectations of the woman he wants to marry.
So I'd present both Rafael's and my thoughts to him and ask him what he wants to do. You also may have a good challenge to find the right therapist in Hong Kong, but at least you should be able to find someone who's got a good grasp on different cultural models for manhood.
Respond if you have any questions you'd like to discuss--and perhaps Rafael and I can discuss with each other on here as well.