First off, I'm sorry that you have to deal with the frustration of not hearing from him. But for your sake, I think you need to let this one go. From experience, I can say that a guy who flakes or just disappears for long periods of time is not a reliable partner. A guy who falls off the face of the earth is usually seeing multiple girls and isn't interested in a commitment. Ultimately, what you want is a guy who cares enough about your feelings not to just disappear without any explanation, and this guy isn't it.
If you're looking for something long-term, there's absolutely nothing wrong with telling him that. The truth is, your telling him that isn't going to change his opinion of the relationship or where he wants it to go. A guy either wants to be with you for the long-term or he doesn't.