Be yourself. If you are up to it, flirt back. Whatever you do, do not discuss the relationship w/him. Just be careful and keep your eyes and ears open. Generally when they are nice, they've been up to something or getting ready to slam us w/something. Hopefully your h isn't going to be one of those who does this.
What you are seeing is the flip side of his personality. They do this most of the time...anger, nasty, etc. one time and a few days later, when they think things have cooled down....pleasant, acting as if nothing is wrong. One thing...we don't forget has nuts they act.
Listen to what he tells you and sift through the conversation later on...you might be able to pick up on some things you weren't aware of until then.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.