I would suggest that you read the works of two important authors: Abraham Maslow and M. Scott Peck. Abraham Maslow is important because he studied the characteristics of self-actualizing individuals. Those in the process of self-actualization are thought to be the mentally healthiest individuals. Reviewing those characteristics may provide guidance about how to live, think and view the world.
M. Scott Peck’s most famous work, The Road Less Traveled, is a classic and timeless book. Peck discusses common life problems. He addresses anxiety, depression and how one can change their attitude to improve their life. I would highly recommend it.
In your letter, you provided a rationale for your depression. For example, you and your parents no longer share the same thoughts, opinions and values. You see that as something negative but in reality, nothing is more important than becoming an independent thinker. Maslow observes that many non-self-actualizing individuals don’t know their own thoughts, opinions or values. “Too many people don’t make up their own minds but have their minds made up for them by salesmen, advertisers, parents, propagandists, TV, newspapers, and so on.” In other words, they are not thinking for themselves. The fact the you are beginning to develop your own identity is a sign of growth but that is inconsistent with suicidal ideation.
You are also concerned about not having developed quality friendships. It is very difficult to form true friendships. It is easy to have work friends, school friends, etc. Though those relationships appear to be very real, they are almost always based on convenience. When you are no longer going to school together or working together, they almost always end.
Don’t assume that something is wrong with you. It may be that as you grow and change your values and interests are also changing. That is perfectly normal. In addition, very few people maintain deep personal connections to childhood or adolescent friends. People grow and change and they move apart. That’s the norm.
You also stated another area of concern; never having had a serious relationship. For you that is a sign that something is wrong. An alternative and more realistic explanation may be that you have yet to find the right person to devote your love, time and energy to. That same logic could apply to friendships.
Whenever someone has suicidal thoughts, they should seek therapy. One can be down. Life can be hard. Though this can be endured and may even be necessary to do so, suicidal thoughts are not normal and should never be ignored. Don’t hesitate to see a professional. If you had a rash on your skin, you could read many books on dermatology, take classes at a university and study case histories. I have no doubt you could learn to treat your skin condition but in essence you have done all of the work necessary to become a dermatologist. It would have been much easier to have gone to a specialist who has already done the many years of study. Learning to fish is a relatively easy thing. Learning to diagnose and treat depression is not. Please do not ignore your suicidal thoughts and feelings. They should be brought to the attention of a qualified professional.
I have limited information about your life and history. Thus, my response is limited but a therapist could take the time to learn many details about your life and provide a more thorough analysis. Therapy could also help you to move past this difficult period in your life. I wish you the best luck. Please take care.