For god's sake - for your OWN self-esteem you need to slap this nonsense down right now.
He gets to pick? REALLY? You honestly think that it would be possible to hear him say 'Oooh, I guess you're the one! Congratulations!' and go back to living with him, and sleeping with him, and not spend the rest of your life hating him with every fibre of your being and hating yourself more???
What you need to do, right now, in order for your self esteem to survive this, no matter WHAT your belief of the situation is, is to text him right now and say
'Thought it was fair to tell you before you waste any more time deliberating your 'choice' this weekend. I've made my decision. I absolutely don't want you. No -one worth having, mid-life crisis or not, would ever act like this, and I am worth so much more than a 'man' like you. Hopefully for you, OW's standards are lower, or I gues you are in for a lonely Christmas. Regards.'
Send it. Don't think about it, send it.
Whatever happens in the future with this prick, if you give him the opportunity to call and tell you the 'result' of his decision before getting in there first, you'll regret it forever.