Is this his warning sign?

Yes that is it exactly. He obviously feels completely unimportant in your life. He feels like he is the last person/thing on your list of priorities. You need to decide if you have time for a boyfriend and if you even really want one. If you do then you are going to have to commit a little. You will have to Make time for him, make plans, phone calls, etc. Being a good girlfriend means really being there for him and him being there for you. If that is something you just can't do then you should honestly just tell him that you are sorry but you can't handle that kind of relationship right now. It's not fair for only one person to be happy and getting what they want from the relationship. Good luck.