I think the only way you're going to be able to do this is to see if he'd be willing to be on a complete "no contact" and "transparency" plan with you. New cellphone #, with detailed billing coming to you, a keylogger on the home computer, GPS on his car if necessary, no-contact letter(s) to any OW, etc.
Plus counseling for sexual addiction.
With no children involved (smart), and considering his past history, I'd insist on nothing short of 100% of this, or you're right -- he WON'T take you seriously, and it will only happen again.
