I am so sorry you have been through this, Tearsofthemushroom, him cheating, leaving and then just as you were starting (as you say) "to feel that there was light at the end of the tunnel", he has put you through some more hell!
Please don't wait for him to 'choose'.
If he chose you, you wouldn't feel good, because he still wouldn't face what he has done. He would continue to put you through hell and your marriage would still end, the only difference being that it would be a bit further down the line, and you would be a lot weaker. You know that is true.
If he didn't chose you, he would have been allowed to throw even more pain in your direction, eroding the hard earned gains you have achieved in those two months. Remember the light at the end of the tunnel?
Please, don't let him him choose, Tearsofthemushroom. Contact him today (email, pm) and simply say ...
"Exes-name. You lied, you cheated, you committed adultery, you ended our twenty years of marriage and you left me. Let's leave it at that. The choice is now mine. Tearsofthemushroom"
Send the message, you will feel your own strength, and you will find that your light is still there at the end of that tunnel.