No - you are not blowing this out of proportion. She belongs to his past, and it is a part of his past that he should close the door on.

He wants to maintain a relationship with her. This isn't him talking about a past relationship. He is actively cultivating a current relationship. Tell him it is high time he cut the tie. Do not allow him to talk to you about her. Tell him he absolutely must not be arranging to meet with her for any reason whatsoever. Tell him that he is jeopardizing the staility of his marriage by doing this.

Make this non-negotiable. You and he have a daughter. Of course you want your marriage and family to remain intact. What he's doing is 1000% inappropriate - to say the least. Put your foot down. You not doing that is enabling him.

He should know better, but he doesn't. You do, so tell him you will not tolerate any more of this. He's treating you like a fool.

He should stop following her on facebook.