Thank you for writing in to Just Answer.
What you describe sounds like a sort of adult separation anxiety
and a strong emotional dependence on the other person so that his physical absence is painful and the thought of loosing him is very threatening.
It is obvious that the two of you share a deep connection and feel very attached to each other. At the same time, the constant worry about loosing him is eating into your happiness and is something that I would recommend that you address with a professional therapist.
It is possible that certain unresolved issues from your past (childhood, adolescence) could be springing up now and causing this anxiety and creating this feeling of emotional dependence. Psycholoanalytic psychotherapy is recommended for uncovering those past issues that are at the root of how you feel.
Once those issues are resolved you would typically see yourself enjoying your love/relationship but not being worried about it ending. Also, the anxiety you feel when you're separated from him would reduce significantly so as to not cause any stress
I hope I was able to provide some perspective.
Please do feel free to reply with any thoughts/questions you might have.