Lady...This is so disturbing. I went thru a similar exp with an alcoholic/addict. He wasn't computer savvy and no pictures were involved, but he was very persistent in harassing me. In my case, he turned dangerous, breaking into my house with a gun and trying to shoot me, which ended with a standoff with several cop cars in the neighbor's driveway. This fella you describe sounds equally unbalanced. I mean, really!...he thinks he can threaten you into resuming your relationship..out of fear! I seriously recommend you put all evidence, however vague it may sound to you, on a flashdrive and go to the police...SOON!
If you get no support from the police, call the local court system. Our courts have personnel devoted exclusively to cyber safety (and this is a fairly rural county). They have even come to my classroom and talked to the students up close and personal about such issues.

Like you, I wanted my bad situation to end quietly. It didn't. Stalkers are all about control, you know. The boy you are describing isn't reasonable or rational. You are rational, and you are hoping rational thinking will eventually reason with him. It won't!