Inclusion of a non-contributor co-author On the last day before the submission of our paper, a Ph.D. student in my group got her name added on the paper. She did not do anything but reformulate a sentence in our manuscript. I replied to that decision saying that I was surprised to see her name on our paper. 

And now I feel horrible. I did not talk to other colleagues in the same lab about this, because of I afraid I might blame her. However, when I came back to work, other colleagues (even the one who is not related) came and asked me why I was sad about that. I then understood that I made her hurt a lot by being surprised at the decision and that she had to talk to our colleagues to clear her image. 

She said that she didn't take anything away from me as I am still the first author, that she couldn't care less about the paper and that I made her a wrong person. She could not understand why I took such an importance on the coauthorship. 

I do not know why I was that sad about it, or why did I value my works that much. I was too egocentric and egoistic, but even until now, I could not make my feelings of unfairness go away. I do not know why I am that sad. Maybe it was because I did a lot experimentally and numerically I felt entitled. I do not even know, and I was just really sad. 

I always say I want to help her with the experiment and works and everything as I am finishing my Ph.D., but I do not understand why I couldn't be happy helping her by having her name on my paper. 

My feelings are really weird. I felt so wrong on something that shouldn't be a big deal. I only cause hurt to people, everywhere I go. I want to disappear. 

In general, my existence in the scientific workplace is wrong. The boys always say that I was not normal and that I have sexuality's problems because I refuse to date them and remain single. The girls always say that I was slutty because my classmates and co-workers are mostly male. But other people did not have such problems to blend in and did not cause so much pain to others. Because of me, people do things they do not usually do, such as sexually harassing me or verbally abusing me. Maybe it was the way I dress, or the way I talk, or the way I work. I made others unhappy. I only victimize myself while I was probably the main reason for every sadness. 

People were so happy without me, and I have to come to disturb everyone. I can not be an egoist and remain. Why can I not die, is it because I am a hostage of life? I'm still chained to my family. But I hate myself so much. Why am I like this? 

I just want to vent, I guess. I am sorry for saying all of this nonsense, because, the problem was just me
I'm sorry to hear all of this (and also sorry about the downvotes without hints how to improve the question (but sometimes they seem to be just a way to greet new users in this site)).

It was right to question the authorship. On this site you can find many good answers on this topic.

I have two hints for you: first, as Mr. Eldredge says in the comments, please see a therapist. Your problems are far too serious, you need someone to talk to.
Moreover, please look that academia is not your complete life. Do other things in your spare time that fulfill you. Don't work too hard. Spend time with hobbies and friends. Then problems at work/university will be not so important as they seem.

Good luck! I give you morally 1000 upvotes and wish for your best!

Edit: I don't know whether it is allowed to say here, but there is also "AskAcademia" on Reddit. My opinion: The topic is similar to this site, but the people there are much more "human" than here and in general, friendlier. (The quality of answers is not always so high as here, though.)