I don't see anything in what you've said that indicates that he was using you. Most relationships fail, and since you two were 6 hours away from each other, he may have thought that it wasn't worth pursuing for that reason alone. I wouldn't think too much about it. The truth is that you will never know what was going on with him. Maybe the relationship between you just ran its course. Maybe he met someone in person (long distance relationships are BEYOND difficult, so not only does the chemistry have to be there, but also the desire to put up with the drawbacks of not being able to see your SO on a frequent basis). I'd just let it go and not overthink it all.