I'm not sure this is a law question, but I'll try to answer it anyway.
First, anyone (teen, a college kid, a great-grandmother) who is depressed for any reason (sexting, loneliness, the death of a friend) should see a therapist. There's no harm in talking to an expert.
Second, lawyers tend to be a very depressed bunch. If you do end up studying the law and passing the bar, I *highly* recommend the book "The Happy Lawyer" as a primer on maintaining your mental health. If you're attention span is too short for a whole book, the Web has plenty of shorter articles on the subject. For example: http://m.psychologytoday.com/blog/therapy-matters/201105/the-depressed-lawyer
I don't know if it is not the other way: people who sext are more likely to be depressed. Depression can cause people to do things they would not otherwise do if they were not depressed. Depression is most often associated with unhappiness about one's lot in life. People are unhappy because their lives aren't going the way they want them too. Therefore, they oftentimes look for an escape (a fantasy). Sexting and other unhealthy sexual behaviors can provide that fantasy escape from their unsatisfactory, depressing reality.
Moreover, people who don't like themselves may act out in this way. A girl who believes that she is pretty but stupid (or otherwise unworthy in some way) may turn to sexting as an avenue for attaining the "positive" attention she craves.
Not everyone who sexts is depressed. Their are couples that sext as a way of expressing their sexuality (or as a way to flirt with each other). However, if these texts are not wanted by the recieving party, are misused by one of the original parties, or either party is underage, these persons could be facing criminal charges.
You may want to repost this question in the medical section. There might be some psychiatrists out there who could also way in on this subject. My knowledge of this subject is limited to my experience prosecuting sex crimes in my former career.
Interesting question. Your answer is . . .
Wait a minute, so you want to be a lawyer? One of the hallmarks of a good lawyer, and the great lawyer is a natural curiosity. You exhibit that. One of the hallmarks of lawyers who make a difference is the willingness to take on a task by planning, thought, and careful and deliberate study. The general public does not usually see value in this ('mental work'), only in results. Some lawyers call it 'work', and some call it fun. The knowledge gained from study can be used to help people. Another hallmark of the curious researcher lawyer is that he or she does not simply accept what is stated as fact, but evaluates the 'fact' with his or her own study. Here is your opportunity to begin training yourself to help people. If I write out the information now simply for your time in reading in this, you have gained nothing because you have given nothing. Your answer awaits you. The question is important to you enough to post it in a public forum frequented by persons with education and life experience. Is it important enough to you to make it a priority for action in your time today?
No attorney-client relationship implied or accepted without a signed fee agreement. This response is theoretical only and for purposes of discussion. Attorney is not liable for any opinion expressed herein.