He may still be really worried what you think of him, or if you are going to break up with him suddenly. As you pointed out, there could just be other things going on, like maybe family problems, as an example. What I think would be most helpful in this situation is if you just ask him what's on his mind and reassure his fears. Don't try to push him to talk too much at first cause that may scare him away. But let him know that whatever is on his mind he can trust you, and that you care about whatever it is even if he thinks that it might sound silly, assure him that you won't think it is. Express your feelings to him and let him what he means to you. Then maybe he will feel more comfortable opening up to you.
Also, please realize that you should wait a little while before you decide that this is love. Love is a strong word at any age, and at 13 it's tough to know about. Keep in mind that emotions change quickly at your age, and they should be taken with a grain of salt. And not rushed...
I hope this helps you