Hi Gianna,
Being busy is not a good enough excuse to justify not messaging you more consistently.
Although he seems interested, he really isn’t. Any guy, even those you meet locally online, would be more consistent in messaging you if he was truly interested. He would want to learn more about you. He would want you to learn more about him.
He seems interested whenever he chats with you because he wants you to feel as though he is interested. He only does this to keep you engaged so as to have you as an option in case he is unable to meet someone else of higher desirability.
He hasn’t blocked you for the same reason. He wants to keep you around as a possible option.
It isn’t wise to stick around hoping that he starts messaging you more. The longer you stick around, the more likely you become emotionally attached and that isn’t a good idea. Move on from this guy. He isn’t truly interested in you.