Although I am 26 and single, I went through a similar challenge, not with a girlfriend but rather with my family. I had visions of ‘Freedom 30’ for a while, but thankfully never really got consumed by the business as the people and environment always kind of turned me off, not to mention the fact that I saw my family doing everything they were told for years, busting their butts, and maybe making a slight profit. This is despite the fact that the diamonds will feed you cliches like ‘the business is 100% predictable’, and ‘no one that has done everything required has ever failed’. Those statements are simply not true. The business literally consumed my family for a number of years, things are starting to show improvements as of late thank goodness!
Support your boyfriend, and say you care about his best interests. Try and introduce him to what is truly ‘the big picture’ . Try and make him understand that the information that he is being presented is very one sided, and not objective. Try and get some credible info from the other side into his hands. Personally I found the Bo Short (ex diamond who resigned for ethical reasons, do a search and you should find his name) resignation letter worked wonders as my family viewed his word as credible. The recent Don Storms and Joe and Doris Shaw situations also don’t look good for the business. Point out that many diamonds have either resigned, been terminated or just had their business collapse, hence going back to former careers. Connect that with the fact that the residual income theory is a myth. Why would many diamonds have gone back to work if a six figure salary just rolled in every year? Try and make him understand that if he will be big in the business he will have a lifelong commitment(at least as long as the business exists!) to it focused largely on the sale of tools and that he will likely be a very busy guy, not kicking his feet up on some tropical beach. Again, the Bo Short letter covers all of his and much more, it is a must read. The upcoming Dateline show would be recommended as well.
Agree with most of the previous posts, get at your boyfriend sooner rather than later, as the commitment will only grow, and could consume him for years. Get him the objective info that I suggested above, show him what he could do with the money he will be wasting on training materials, and if he is an aspiring entrepreneur help introduce him to other potential business models that will almost certainly have a better success potential than Quixtar.
If none of this works, and he truly becomes more devoted to Quixtar than you, than I guess you would have to think long and hard about your relationship!