A friend of mine is mourning a loss of a Weixin friend

A Week ago, Andy found Nina through a social app called Weixin. The similarities between them immediately drew them closer. They belonged to the same constellation sign, they made each other laugh, they shared the same loneliness in life, and each of them was trapped in a troubled and unfulfilling relationship with someone else. They found they could freely talk about their personal feelings with each other that were hard to share with others around them. They gave honest and sincere (advice) (The word advice is usually singular, I never heard it in the plural form.) to help each other cope with their separate realities. The feeling of connectedness was almost like talking to one’s own conscience. Also the rhythm of the dialogue back and forth and the way they complement each other was like an experienced couple dancing on the stage.
Andy’s long, busy day at work had soon become much more enjoyable. He would squeeze some typing breaks here and there in between meetings and miscellaneous tasks. His smartphone had become his tiny sanctuary, his oxygen tank and in it Nina was his air and his sweet conscience.(Beautuful sentence) 

Until one day Mandy found out about Andy’s past conversation on his phone and was sad and furious. Her pain and fury were chiefly based on the fact that Andy had so much personal feelings to share with another female found on the web than with her, his wife (I would not use two pronouns referring to the same person because it's redundant, I would say "another femal found on the web than his wife"). Out of her self-protective instinct, Mandy made him delete Nina from the app. Wanting to salvage someone who he considered a soul mate, Andy explained that it was an innocent friendship and would like to maintain the status quo but to no avail.

When told from Andy about what had happened, Nina was suddenly attacked by so much guilt that she insisted ending their Weixin correspondence which now she considered as immoral.

After the incident subsided, Andy and Mandy called it truce. He went back to his normal life with only half a soul. He found it harder to concentrate at work and felt a part of him had just died. He felt the homophobic (Do you mean the society is against gay (homosexual) people, or is it the fact that Andy can't share his feelings with other guys without it being labeled as "gay") culture as we live in today somehow made it harder for guys to reveal their soft spots with one another. Andy felt suffocated and didn’t what else he should do to ease his pain.

What should people do when they realized the difference between they and their partners seem to be too big to bridge? Is it so much a sin to have a spiritual connection with an opposite sex outside the marital bound?

I think that people should get counseling or if it's the worst case scenario where the marriage will not work out, they should get an amicable divorce. I think it's wrong to have a relationship outside marital bounds because it's considered emotional cheating because the person is replacing the emotional connection with the spouse with another person and that's a form of betrayal. 

I am curious what your definition of a sin is, because in the United States the word sin is really only used in a religious context and may refer to a vice that is not looked upon as good by a church but is not necessarily considered wrong by society. 

¡Hola! Iré a una cena.

Hola. ¿Cómo están? Esta noche, mi amigo y yo iremos a una cena para conocer a un abrogado. Él es un abrogado muy importante porque él va a postularse para un cargo en nuestro estado. En esta restaurante, comeré pollo. Mi deseo es que voy a divirtiese.