Breaking via text msg is a cowards way. We don't know all the facts why he was treating you badly, highly possible that you were treating him badly too, however, your actions show that you are not a victim, you are certainly a coward, but not a victim.
Answering to your question, it is hard to give 'yes' or 'no' answer. Theoretically, you were not cheating, but practically you did cheat on him.