Maybe he was tired and accidentally deleted your last message or forgot to hit send on his. I would just text him again. No biggie.
If you do decide to break up with him, make sure you call him on the phone to do it. Even it means have to pay for a long-distance call. Breaking up with somebody you've been seeing for six months over text is cruel.
“This planet has - or rather had - a problem, which was this: most of the people living on it were unhappy for pretty much of the time. Many solutions were suggested for this problem, but most of these were largely concerned with the movement of small green pieces of paper, which was odd because on the whole it wasn't the small green pieces of paper that were unhappy.” ― Douglas Adams, The Hitchhiker's Guide to the Galaxy