You are clearly a thoughtful and insightful person. If you could solve this problem by yourself, you would have done so already. For that reason, I think you should see a therapist — both for a more thorough evaluation and to explore options for treatment.
I’m not at all sure that the problem is one of attachment. Maybe. But there are other diagnoses that share the same symptoms. Borderline Personality Disorder and Bipolar disorder are a couple of the other possibilities. A treatment is only effective if it is addressing the issue. Do make sure you are being treated for the right problem.
Please take care of yourself. You are only 20. If you get proper treatment now, you can have a long life with satisfying relationships.
I wish you well.