The sex hormones testosterone, estrogen and dopamine, and the associated neurotransmitters that act upon the nucleus accumbens, regulate libido in humans. These chemicals are either naturally released so that we experience lust and desire to make babies, or heightened when we are sexually attracted, infatuated, and fall in love. The frequency and amount of the release is influenced by genetic, biological, medical, social, psychological, and spiritual factors.
Genetically, some people have a higher or lower libido than others. Biologically age and physical health plays a big role. Social factors include stress at work, and with family or friends impact libido. Psychological challenges include unresolved trauma, sexual abuse, relationship conflicts, personality disorders, and psychiatric illnesses often lower libido. Adverse medical conditions, medications, pregnancy, child rearing, menopause and certain legal and illegal drugs, including nicotine and alcohol, lower sex hormones. Evolving spiritually can lower our sex drive if it leads to repression, dissociation, or dogmata to be celibate, or increase it through reducing stress, fear, and shame, and promoting tantric practices and sacred sexuality.
As we see, sexual desire is a very complex matter, so we can easily confuse cause and effect. Only differentiating and integrating all aspects can give you a clear answer, especially if you want to regain sexual desire and vitality or support your partner in reviving it.