Geez, Emily, stop it for a minute!!!! If you don't want him back, then fine - you can tell him in 24 hours, okay? But the REAL problem here is your fear of being vulnerable. You are afraid of being hurt again by him leaving again - so you are attempting to control that fear by leaving him first. Does this make any sense? It does NOT get you closer to your goals.
If the problem is that you don't trust what he is currently saying to you - stop and think what it would take for you to be comfortable. What do you need from him? Then write it down and tell him - "this is what it will take to put our R back together".
BTW - it always takes a little time for that final break from OW to happen. And you are ASSuming big time that just because he has to take another call, it means he's talking to her!
Calm down, quit clinging, get on with your life and quit focusing on him. Give it 6 months, okay???