OP you seem to be flip flopping a bit now, and if you carry on this is going to lead you to make bad decisions.
In truth I think you've had doubts for a while about this relationship, from what you've written you've got a full diary, you say you have something to do every night... How would a relationship fit into that? Realistically? The phone business sounds very bizarre... What guy goes into dating, but doesn't bother to look at or charge his phone? In this day and age that's somewhat strange. It seems he's assumed things were casual and he'd see you when you'd planned. It's as if he'd set his stall out with his phone explanations so he didn't have to encounter surprise calls. You seemed to have left the exclusive chat a long time, he really had it all boxed off to be honest.
You keep saying you're not fussed, that you didn't want to be, or didn't feel ready to be his girlfriend, but then you're asking about not dating others... Being exclusive kind of means just that. You're not dating/sleeping/ contacting others. On the flip side of that you're saying hopefully you'll meet the right guy someday. Which is it? I think you need to set clearer boundaries for yourself.
It's not fair what he's done, and nobody deserves to be ghosted. But you've got to be far more positive in yourself. Don't settle for anything less than you deserve.
I don't think messaging him for closure is going to bring any closure, as you say you've deleted him, but then day you're off out with the girls and will enjoy yourself and forget him. In the next breath you're asking should you send one last message, and you're feeling angry. You're either moving on, or you're not. I personally think that phone is a burner phone he uses for dating, he's probably seeing others and with things as they were with you, he kind of had the option of seeing others on the nights he didn't see you. One night a week, or a weekend here and there gave him lots of chances. He obviously thought that suited you too.
If you were to speak to him again, it's likely he'd say just that. He was never asked to be exclusive to you, you in turn say you didn't want an exclusive relationship, but deep down you did. As much as you state otherwise. I think deep down you were trying to mask your insecurities, but went too far, and tried to present a more fun, carefree, living for the moment, and it's kind of back fired, as he's treated you as just that.
Delete his number, be good to yourself. Draw on the therapies you undertook, forget this guy.