This sounds bad on every level. He's got the best of all worlds and is not required to make any kind of commitment to any of them. Your attention is flattering, so he's keeping you on the string to keep his options open. People will only value you as much as you value yourself. They learn to treat you from the respect that you show for yourself and the "price" you set yourself at. (I don't mean that in a sexual sense!).
You are also allowing him to quickly spend your margin of emotional resources, which leaves you without enough to even care for your own needs and will make you more dependent on him. He is afraid of being alone with himself and until he actually gets to the point where he enjoys his own company, he will always be restless and looking to something external to fill that void. No one can do that, and so when he discovers that one person is not the answer, he moves to another, hoping that something or someone will do the trick.
You deserve to be with someone who is able to be physically, mentally and emotionally present in the relationship. That means that his own needs need to be addressed by himself first so that he's got something in addition left to give to you. Someone who is that insecure is going to act in selfish and destructive ways, despite themselves. It's tempting when you understand why the person has those insecurities to keep hanging on because you see their potential and you don't blame them for being in the state they are in. However, it doesn't negate the absolute destructiveness and devastating effect of those behaviours, whether wielded intentionally or not.
This is not as easy as just deciding not to spend time with him. Emotions will always trump reason and logic. Emotions grow through proximity. Proximity becomes like some kind of drug that you seek out, even after you can see that the other person isn't good for you or isn't available enough to be in a relationship. You will need to have enough other people and activities in your life to reduce the amount of importance he has taken on. You also need to cut off contact for a long while until the emotions involved die down as well and become more manageable. Otherwise you will end up pursuing behaviours that you are angry at yourself for, but just can't prevent yourself from doing, and you will accept increasingly disrespectful and inconsiderate behaviour gratefully even if you understand intellectually what is wrong with it. This ends up tying you into an endless cycle of staying to prove to yourself and others that he really does care, and leaves you in the position of not possessing equal power in the relationship and therefore being a beggar instead of a chooser.