Answer:
   
   First, let's look at the obligations that the Torah places on men:
     * They are not to have sex with their wife while she is
       menstruating, and for a specific period after the menstruation
       ceases and the birth of a child. During the menstruation period
       and similarly related prohibited periods, the wife is said to be
       "niddah".
     * They are not to commit sexual transgressions, that is, have sex
       out of marriage or commit adultery.
       
   The Shulchan Aruch in Even haEzer Chapter 21 talks about the
   requirement of men being far from women lest men feel tempted to sin.
   This even goes as far as to forbid gazing (not to be confused with
   "looking at") women. This prohibition is also part of the idea of men
   not touching women. There are those who hold that for men to touch
   women (other than their wife at a permitted time) in any romantic way
   ("derech chibba") is a Toraitic prohibition, as all women must be
   presumed to be in nidda (even when a woman is not having her period,
   she is still in nida if she has not been to the mikvah.).Given all of
   this, the Talmud specifies a number of restrictions to prevent men
   from transgressing:
    1. A man and his woman are not allowed to touch, if they are neither
       related nor married. This is because of the fear that touching
       might lead to sexual transgressions. As an extension of this,
       Orthodox men aren't supposed to sit next to women to which they
       are neither related nor married.
    2. A husband and wife may not touch if the woman is menstruating, or
       for a specified period after menstruation/childbirth (the length
       of the period varies depending on the sex of the child). This is
       because they are forbidden to have sex during this time, and the
       thought is that if the husband and wife touch in any way, they may
       be too strongly tempted.
       Hence, during "niddah" (the time of the women's menstrual flow),
       additional restrictions are in place. These extra stringencies
       apply because the couple is already intimate; presumably, it
       doesn't take much to lead to "the act". These stringencies
       include:
          + They cannot touch (even indirectly using an intermediate
            object).
          + They cannot handle an object at the same time.
          + They cannot sit together on an object that moves (a swing
            etc..).
          + They cannot eat from the same plate.
          + They cannot serve food to each other.
          + They must sleep in separate beds.
          + They may not engage in flirtatious behavior.
          + Although spouses must continue to dress attractively, they
            cannot dress provacatively.
          + They should cover parts of the body that are normally
            uncovered only in front of their spouse.
          + They should not wear perfume, cologne, etc.
       The only exception to these restrictions is pikuach nefesh (to
       save a life). More information can be found in [5]Secret of Jewish
       Femininity.
       As a result of this, many couples that observe these laws sleep on
       twin beds (pushed together during non-Niddah periods and during
       the day, so as not to make the status public). Sometimes, "fences"
       are used, such as one partner putting down something so the other
       can pick it up.
    3. Men and women shouldn't be mixed during prayer. This is because
       the presence of the opposite sex is thought to be distracting
       during prayer. Additionally, a person ought to pray from an
       orientation of aloneness, as opposed to completeness.