WARNING: Armchair psychology to follow!
Long ago, a therapist once described to me what happens in households similar to ours ("ours" meaning yours and mine and whoever else is reading this who can identify).
It goes something like this: you seek affection/attention/emotional connection of some sort. You are consistently disappointed because you don't get what you need (emotional connection is a human need, honest). So as you are growing up, you learn to put a lead blanket over all your emotions - that way you can't be hurt. Nobody can get to your emotions under that lead blanket.
Now you have a girlfriend (or platonic friend for that matter) and they want contact. They want to connect with you. But that means you have to lift up your lead blanket and let some of your emotions escape. And that, quite frankly, is terrifying. So you tamp that blanket down harder, and your friend tries harder to burrow under the blanket. This goes on until one of the two of you finally snaps and the relationship ends.
As for how to gently and safely remove said blanket - that's a much more difficult thing to do. You could start by challenging yourself to find one thing (thing, not person) that you like and admitting to yourself that you truly like it. Or seeking out things you enjoy and that would make you feel happy if you could let a little happy out of your lead blanket. Start with things first. Move on to people after you get to where you can enjoy or dislike something openly and honestly (truly enjoy, not hide in, not run away from, but be at peace with your emotions).
I would very highly recommend finding a professional to help you out here. I was you when I was younger. I promise there is a whole world full of amazing things out there to enjoy, including the connections with others.