Note: this question may have a strong Indian context, but I am looking for inputs from members all over the world.
Eight years ago a close friend of mine, aged 30 at the time, met an 18-year-old girl who later became his sister. This is India, remember, and it happens here. [In India, this is a rather common practice, especially in North India and among students: when somebody feels sisterly towards someone, they may formally tell the person that they will become siblings. It means that a sibling bond can occur between non-related individuals by mutual agreement. However, the people in this question belong to South India, where this is much less common and not really a tradition.]
They were very emotionally attached to each other for nearly five years – just like real siblings – although communication was mainly through text messages. Eventually, she got married at 23 to somebody aged probably 26, and she and her husband are apparently happily married with a 2-year-old infant child.
My friend allowed his communication with her to taper off after her marriage, for fear that her husband might mistrust the unofficial sibling relationship – he wants to do nothing to potentially disrupt her married life. However, he is conflicted because he misses her terribly and feels she might think that he no longer cares for her.
The siblings belong to different religions, which is still a barrier to social acceptance of any relationship here. Moreover, the sibling relationship between unrelated individuals, which carries significant validity in North India, is nearly unrecognized in South India and carries no automatic social validity.
Due to innate mistrust of social attitudes, both instinctively concealed this unconventional friendship from their respective families, and the girl has never introduced her unofficial brother to her husband. It is a fact that husbands tend to be jealous and possessive.
My friend has always felt helpless due to his unofficial sibling status, in terms of being able to be a presence in her life, and he constantly worries that the husband or some other relative will refuse to accept the basis of this sibling connection, which could have serious complications in a conservative-minded society.
Since I knew the girl in question a few years back (but no communication for years), my friend has asked my advice. Should he try to resume e-mail contact with her? My response was weak: "If she were my sister, I too would worry about the husband's mistrust..., but let me think a bit about it." So, I need some good inputs within a few days from the relationship gurus at Interpersonal.SE!