This is from the book...The Sexual Healing Journey...by Wendy Maltz. These are from the chapter in the book "identifying the sexual impact".

Sexual abuse generates negative, false attitudes about sex. These become hidden from your consciousness. you may have difficulty separating abusive sex from healthy sex. Offenders contaminate victims imprinting them with an abusive way of thinking about sex, a sexual abuse mind-set. This mind-set can affect every aspect of a victim's sexuality: sexual drive, sexual expression roles, intimate relationships, knowledge of sexual functioning, and sense of morality.

Sexual abuse, and its consequences, can unconsciously influence how you feel about yourself and about sex. You may now see yourself as sexually damaged, suffering a poor sexual self-concept. Or you may have developed a self-concept that is inflated, where you believe you're more powerful as a result of sex. Knowing how you view yourself as a sexual person is fundamental to eventually making changes in your sexual behavior.

Sexual abuse can create a conditioned way of reacting to touch and sex. Some survivors get panicky, avoid sexual possibilities, and want to run the other way when sexually approached. Others freeze and feel helpless and unable to protect themselves. Still others get overexcited and may recklessly seek dangerous sexual encounters. You may experience spontaneous reactions to sex that cause you to numb sexual feelings, to divorce your mind from what is happening physically, or to become sexually aroused in inappropriate ways. Sexual settings and contact can bring back negative feelings associated with abuse. Flashbacks to sexual abuse may arise and interfere with sexual relating and satisfaction.

Sexual abuse can shatter our capacity for healthy sex. You may have been taught abusive patterns of sexual behavior and introduced to unhealthy, compulsive, abnormal sexual activities. Now as a reaction you may associate your sexual expression with secrecy and shame. Some survivors may withdraw from sex, preventing any fresh discovery of healthy sex. Other survivors may become preoccupied and driven by sex. Sometimes survivors reenact the abuse in an unconscious attempt to resolve deep-seated emotional conflict related to the original abuse. These reactions need to be identified so you can better understand your behavior and eventually work toward healthy changes.

Sexual abuse influences a survivor's ability to establish and maintain healthy sexual relationships. Abuse can interfere with our ability to make good choices. Some survivors may have difficulty finding partners who are emotionally supportive. Other survivors may be unable to trust and feel safe with intimate partners who do care. Survivors may fear intimacy or have a limited capacity to experience closeness. The sexual difficulties a survivor may have as a result of abuse often create emotional and sexual problems for the partner. Knowing where relationship difficulties lie, and how abuse has caused problems, can help you work with your partner to solve individual concerns and to build a more intimate relationship together.

Sexual abuse can create specific problems with sexual functioning. Abuse may have taught you unhealthy patterns of responding to sexual stimulation. Stress and anxiety that originated with abuse may continue to shadow your sexual activity. Over time these sexual problems interfere with intimacy and long-term sexual satisfaction. As you identify problem areas in how you function sexually now, you are also identifying specific sexual concerns to work on in the healing process.

This is a shortened version of what the book says. I hope this can help both BS and WS see the impact sexual abuse has on its victims. It doesn't make the infidelity ok by any means. I just hope this helps you with "why" the infidelity occurred. I recommend this book to anyone dealing with these issues.