You two will get together with him and trade notes. You will find out a whole mess of more lies he shoveled at you earlier. The OW will make a huge pile of demands on his time, he will try to fool the both of you and it will just be a huge mess.
If he thinks you three meeting together is going to resolve anything when he's done zero work to demonstrate he means business he's fooling himself too.
Someone on here told me of an actual FT that suggested this to one couple... inviting the OW into the therapy session to help the WH make a decision... THAT sounded ridiculous at the time and so does this...
Just STAY AWAY FROM HIM... this is all a game to him at this point and he is playing it well.
I seriously think she dumped him/threw him out because he wouldn't let her live with him.
How on earth can he use your facebook status as a yardstick to how bad it's gotten? Does a mountain of lies and manipulation not measure for anything? That statement alone shows you he has no idea how much damage lies do to people. You need to know he understands the FULL GRAVITY of dishonesty... in his words even from that phone call he does not.
I would tell him he has work to do and once he has done that work you will consider him... But do NOT tell him six months or anything. Just let the professionals deal with him.
I would even have him meet your father and apologize there at the six month point and let your father decide if this guy is being honest or not.