Co-authorship nightmare
That is indeed a messy situation. The bad behaviour notwithstanding, I think there's no reason to not honour the initial agreement.

You should retain him as co-author on the intial two papers, without doubt. First, he made the data available to you, and without that these two might not have happened. Second, an gentleman's agreement is exactly that; you don't default only because the other person defaults.

About subsequent papers, I think you should be firm and say no, but also convey and convince X that he is an integral part of the first two papers; that won't change.