Being “head over heels” in love can blind you to the many possible negative attributes of your love interest. In your case, you would like to develop a relationship with a particular person but he may not be interested. I’m also concerned about the intensity of your feelings for this individual. As you stated, “it is killing you, literally.”
It seems as though your life has revolved around this individual despite believing that he is not interested in a relationship. Your blinded devotion has led you to essentially mold your life around his, which has caused you significant physical and psychological pain. From a psychological perspective, this is not healthy.
I would strongly recommend counseling. It is important that you focus on developing a healthy sense of self-esteem. A lack of self-esteem is in all likelihood contributing to your unhealthy attachment to this individual.
You also mentioned that you have BPD which may mean that you have bipolar disorder or borderline personality disorder. In either case your symptoms, if not well controlled, may be contributing to this problem.
I’m also recommending counseling for two other reasons: this problem is significantly interfering with your happiness and you are engaging in self-harm. Self-harm is a sign that someone lacks the ability to solve problems in a psychologically healthy way. I hope that you’re able get the help that you deserve. Please take care.