My fiancee is taking librium for his alcohol withdrawls, how can he wean himself off of it?

Not by himself: If he is using Librium i hope it is being prescribed by a health professional knowledgeable with addiction and withdrawals. If he is getting it some other way this is dangerous, being on Librium too long will create its own addiction to librium. Other non addictive medications may be part of the plan but again doing it on his own is not recommended.

Not necessary: Alcohol withdrawal generally lasts no more than 7-10 days, and Librium takes several weeks to produce its own dependency, so tapering or weaning is unnecessary. In addition, Librium is very long-acting, so in a sense it wears off very slowly and essentially weans itself. He should continue with ongoing counseling and self-help meetings like aa. You should consider going to alanon.