If I understand your question correctly, you want to know whether you have borderline personality disorder vs. major depressive disorder (MDD). You seem to meet some of the criteria for borderline personality disorder and depression. It’s also possible that you have bipolar disorder (vs. your current diagnosis of MDD, not in addition to). Some of your symptoms match that disorder as well. Please keep in mind that I can’t be certain of your diagnosis. I would need to meet with you in person and review your extended personal history, but based on the information provided, borderline personality disorder or bipolar disorder are plausible diagnoses. These are possibilities, not definitive diagnoses.
You also want to know if it’s possible to be born with certain problematic traits or personality characteristics. This is a matter of long historical debate. It is a question of nature vs. nurture. In essence, you want to know if you were born this way or if your environment shaped your personality and led to a mental illness. Science has not determined the answer to this question. Some believe mental illness is purely a brain disorder and the problem is caused by a chemical imbalance. Some believe that behaviors are learned or that our parents and the way we are raised shape our personality. Many theories exist but none have been definitively proved. Many scientists believe that mental illness is a result of a complex combination of biological or genetic risk factors and environmental stimuli.
I usually try to discourage people from focusing on gaining an exact diagnosis. There are two basic “schools of thought” on whether a mental health diagnosis is helpful. On one hand, if an individual suffers from a series of symptoms and then learns there’s a name for this specific set of experiences, it can be a relief. It can also be a validation. On the other hand, learning of a specific diagnosis is not always very informative. Nor is it easy to know whether the diagnosis received is accurate. Mental health diagnosis is not an exact science. In addition, getting a diagnosis may make an individual feel upset, overwhelmed, hopeless, and even stigmatized.
What’s most important is that you find a way to relieve your symptoms and live a happy and fulfilled life. Troublesome symptoms make it difficult to function. It can make life miserable and you unhappy. You may not need medication but at the very least, consider individual therapy. You mentioned that you have problems managing your mood. Therapy can help with this. You also said that you are struggling with relationship/marriage problems. Again, this is the type of issue for which therapy could be very helpful. Try asking your general practitioner (I’m assuming this is what you meant by GP) or your psychiatrist about referral to counseling. You may also want to try searching this therapist directory. Thank you for your question and I wish you the best of luck.