Here is a book recommendation for you: Smart Women/Foolish Choices: Finding the Right Men Avoiding the Wrong Ones
Imho, Bigfluffy , you still see your relationship with him through your age 20 perspective with many layers of filters of Grand Love, he spends money on you (which can be used to justify all sorts of things), he was great with your child, he did " " family holiday" " with you and your child (the Luke Skywalker shot to obliterate your perspective to keep you tuned in to his script). In short, he played you. He Used you.
You saw this and walked away after degrading yourself for two years (kept you secret). Well done, by the way, on seeing there would be no future with him...then. The fact he isn't married now is a red herring. But, I think the 20 year old you has been triggered because at that time, it was a source of great frustration for you... and now you see a way to "victory".
Let's be clear: this is not the kind of victory that you want because he is a Grade A boobie prize. You know what kind of lying, cheating, duplicitous actor he is; and he knows the kind of treatment you will embrace put up with and has probably kept notes for playing you like a grand piano. This is the foundation for your lunch date tomorrow.
Don't trust him, Ok? Anything he will say or do- offer you a job, get you a raise, compliment your work, how fabulous you are, your awesome looks-you should be a movie star, what a wonderful parent you are, how sorry he was when you left, you are the one great regret of his entire life and he would fall to his knees in sobs of gratitude if you could give him one more chance...for, as many previous posters have pointed out, a fuck. Because that is all you are to him. And that is because you agreed to degrade yourself by being his bit on the side while he was married. I dont think that perception is going to change, sorry. Pay your way, Bigfluffy. Dont let him create any implied contracts that you owe him for anything.