In response to Toni Hemmati...
It is commonly believed that human sexual behavior is voluntary and motivationally driven, but I offer some other thoughts...
Research conducted by Nordeen, Yahr, Belchets, Wildt, etc., in the late 1970's and early 1980's look the fact that sex hormones, programmed in our brains at birth, can determine human sexual behavior, in later life??
Money ( 1980, 1986, 1993), states that "human sexuoerotic differentiation and development is incomplete, at birth". He maintains that humans need input from the environment, through senses of touch, vision and hearing, to complete the process. This process begins in the postnatal period, and is completed by puberty. This process determines who we, humans, will be sexually attracted to, in later life. This will also determine the level of paraphilia (legal term for perversion), in later life. He offers much research in mapping out sexual behaviors of individuals who engage in "perversion" (legally speaking), and he offers explanations.
Money further comments that human sexual behavior starts in the womb, and can be observed via sonograms (mostly in males). He goes into patterns of pair-bonding rehearsals of 8 and 9 year olds, and states, that if left (by adults) to "rehearse" normally, this process will lead to normal, well-established sexuoerotic practice in later life". He explains that adult caregivers of children frequently "vandalize" this normal pair-bonding rehearsal, and therefore, cause wounds, that play out, and need to be healed, in later years. Research shows that where children are left alone, to develop normally, the majority will turn out to be heterosexual (Money and Ehrhardt 1972).
It is interesting to note that Money also looks at the concept of what is commonly called sexual "perversion", and offers the thought that non-traditional sexuoerotic interaction may only be perversion if the partners are not offering consent and agreement. The problem then lies in the fact that there is no provision "for what should be done when there is not mutual consent".
Toni, there's tons of research on the subject. It may help you to offer alternative explanations/interventions, to your clients, which may help them gain insight into their behavior.