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Sounds to me if he was serious about being with you, he would make the time for you. Not having time is just an excuse. We make time for things that are important to us. Don't allow yourself to excuse this type of behaviour.
The relationship wasn't working out because he had no time. So you two broke up. Sounds to me like you really want a guy who has time for you and will make time. Not someone who is too busy for you.
Even if you two were good together when you both had time, it doesn't make up for someone who can't or won't make enough time for you. That's a problem and it sounds like you value a guy who will make time.
Also, when you texted him saying you missed him, his response was "idk". That doesn't sound to me like he misses you much.
I say give him some space. Work on yourself and try to move on. Find a guy who will give you time.