It would be helpful to urge your sister-in-law to find a way out on her own from the marriage or the issues that she faces with her husband, your brother.
It is important to be a friend, to be friendly, before demanding it of the other person.
To be happy, we all desire different things. Some people need a lot more connection and communication than others; which fact is not a reflection of or enough grounds to judge anyone as good or bad.
Do keep a few rules in mind for a long distance relationship to work, and to bridge the communication gap.
So your wife, with all her good intentions, might have made a poor choice in the friend she chose. It is understandable that you feel hurt and confused.
You are in a classic fix of having to decide between two important values; your personal happiness and your marriage. It is not uncommon for married couples to live in different cities because of financial or career related reasons.
You can take solace in the fact, that sooner or later, the same is true for the majority of couples, even if you were married to a super model.
Sex is one area of our lives, where wrong choice of words and tone can hurt more than other areas. We feel the most vulnerable in our sexual natures of our bodies.
Today more than ever in the history of marriage, couples have the rights to decide their own rules of engagement.
Communicate about these important things before marriage and achieve those mutually agreed-on goals before you seal things with the stamp of marriage.