I have also been in relationships since I was 15 and am currently struggling with constant fear and worry about my current relationship because I feel I cannot be alone. Even though there are no signs of breaking up I am worried about when it will end. It's awful.
Therefore, I understand why you feel compelled to always be in a relationship and about being "whole". I don't think it's unhealthy to always be in a relationship, only when it becomes something where you don't feel well when you
aren't, which seems to be part of your (and my own) problem.
I don't think you are pathetic, you are obviously allowed to be upset when someone breaks up with you! So much can happen in 3 months and you can't help if you become attatched to someone. But just remember how much happened in those 3 months and move forward to experience all the things that will happen in the next 3 months.
My ex doesn't respond to my texts anymore and at first it upset me. But then I realized he is simply trying to move on and that maybe not getting a response gives me a reason to not care and also move on. Feel better soon.