Is this an indication that he's been considering it?
I don't know your H or your situation, but yes, he has probably been considering it for some time. Sometimes a WS begins an affair as a way to transition out of the marriage. They are looking to have a new support system in place when they decide to leave; especially if they know their current friends and family would not approve of the new AP.
You may find the following book to be helpful:
Uncoupling: Turning Points in Intimate Relationships by Diane Vaughan
This is not an affair book, but it will provide valuable insight as to where relations go wrong and what spouses will do when they are considering leaving the marriage.
So sorry for what you are going through.