While a decline in sexual interest is normal to some degree in many long-term relationships, experts report that resentment is a major cause of libido loss, and it strikes men as well as women. Anger at a partner—for being overly critical, for being too dominant or too passive, for ignoring one's needs, for any reason at all—can dampen sexual desire, and is a culprit that couples therapists often look to address when discussing one person's lack of interest.