Your letter is confusing to me. Why dont you just tell the guy that you have chlamydia? If he starts giving you a hard time about it, just say, "according to MY timelines, you gave it to me. Goodbye."

If he gives you a hard time about it, why would you want to stay with him? I wouldnt mention anything about worrying about your reputation. That just gives him ammunition to use against you. If he is a good guy, he wont say anything anyway. If he is not a good guy, nothing you ask him will make any difference.