I had a friend that had similar issues but wasn't quite that bad (but she had taken a long time to learn coping, and she still had the following issue). She had serious, debilitating, panic-attack inducing abandonment issues.
Actually, she was my best female friend's roommate and at the same time was my best male friend's girlfriend. She was virtually never alone and needed it that way.
One week, both my best friend and dude friend went out of town on a 4-5 day college event trip. And she flat out almost begged me to stay in the room with her....she even went to her roommate beforehand and asked if I could sleep in roommate's bed every night while they were away, so that i would almost always be within a few feet of her barring classes. I was even asked to stay in the room when she went to class if I didn't mind, so that when she came back she wouldn't be alone.
I should point out the following since people will freak: (1) I was totally okay with all of this and it was no trouble, and (2) I was basically allowed to do all these things beforehand, even stay in their room while both of them were in class/dinner/anywhere. I'm male and their both female. That's how close we all were and how much they trusted me. So this wasn't an abusive/manipulative/guilt trip me thing.
I literally spent almost that whole time except class in her room or eating with her or whatever she was doing. She was afraid is she were left alone that whole time that she would be having constant full-blown panic attacks, and she almost had two or three anyway, when they left and again one night when she was alone for a while.
She was really worried about them the whole time, even though I know she dealt really well and had me to help her stay calm. Especially her bf...she was always sort of afraid (even normally) something might happen to him when he was gone too far from home or away a long time or whatever. She wasn't abusive, or manipulative....she was just really scared. And she needed someone to always be with her.
IMPORTANT PART: For what it' worth, they ended up being a perfect match because of that issue. he had always had exes who told him he was worthless, they didn't need him, he was always around too much, he was a worthless bf, they didn't want him around, over and over through many different exes.
When he finally got together with her, it was perfect. Still is. Because she needed someone who was always there and would always want to stay near her, and he needed to be needed that way. He had an intense protective nature, in the best way....and to finally have a GF that said, "I want that. I want you to be that protective of me, i want you to like being around me most of the time"....got him out of a really bad place. He felt totally alone and finally there was someone who almost never wanted him to leave.
I'm not saying all that to say your guy will be like that. It may take some work to help him understand you and your needs....he may not ever understand period, i don't know him. Hopefully he will. I'm saying it to say that thinking and feeling that way....it doesn't make you a bad or messed up person. It's just you atm, and you've done a lot of work on yourself, so don't feel too bad if you can :/
I can't say anything to help in the immediate tense, but just to let you know there is a hope for that and that some people fit with that. Maybe, after you feel the relationship is in an appropriate place, you can show him this post....maybe even our responses, and see what he thinks about it :/
I don't know that he'll understand or that your ship will work out, but i hope it does :/