There... that's good stuff, MrsD... stuff that you can actual work on that will benefit you... AND... might also benefit your possible R with your X... or at least your interactions with him...
You can not take away from the reality that you and your X have "history"... of course, his story and your story about your past M is probably different...
Now... you are GOING to be told that he is cake eating, if you haven't been told that, already.
First... so what...? he stays connected to you... while you are working on yourself...
Second, he isn't cake eating if he's having an EA with you. He's transferring his emotional connection FROM GF TO YOU.
I will tell you... that in a "normal" world... I DO NOT date women who are dating others. But... this world we find ourselves, in our sitches... is not "normal"... unless you base normal on statistics...
You have the edge up on GF because you and your X have a longer history AND... have children together...
Your X is obviously confused... if he clearly wanted nothing from you, he'd not be part of your life. He clearly is not opposed to the physical connection. He clearly is not opposed to the emotional connection...
He is just... scared... scared that... IF... he were to get back with you... that you might betray him, again...
Seriously, rethink your self confidence, because from where I sit, you could easily have your X back... he's attracted to you...
It's YOU... YOU... are afraid, too... His fear is obvious and... you'd probably say... warranted...
You are afraid why? Because you had a weak moment? That you are now a bad person because you did something that you believe you should not have? That you will repeat your mistakes...?
Doesn't sound like it, to me...
Your confidence is low because... you think you are a bad person? You have no idea the history of his GF... she could have committed fraud, or had her own past infidelities, or even worse...