Co-authorship nightmare When I was in my PhD program I started working with an Assistant Prof. X in the department. I collected a large and valuable data set and at some point X "borrowed" me two RAs to clean and to organize the data. X didn't provide any further help, I oversaw the data collection, managed the RAs and did the final checks on the data. After the data was collected, we agreed that we would share authorship in 2 papers involving the data. Then, if I wanted to use the data for any other projects I could use it without including X as a coauthor. X emphasised on several occasions that I didn't need to include X as a co-author in other papers that I started.

The 2 original papers got stuck, partially because X somehow stopped working on academic research and started taking other engagements (e.g. consulting, etc.). Due to this, X's tenure-track position is on the line as X could not make enough publications. I understand that this situation is bad and somehow X has grown "desperate" trying to pull the strings from here and there. 

X came to know that I was using the data for a project that is in advanced rounds in a major journal. X started to emotionally blackmail me and other coauthor to include X on the paper. At the beginning we didn't give in, but finally one of the co-authors gave in and included X in the paper, although he hasn't contributed on anything in this project. Meanwhile, he kept telling others that I did wrong, etc. which isn't true given our initial agreement. 

I don't feel good about this, as I believe one should provide meaningful contribution to deserve authorship. Now X has gone into a non-response mode for months and would not respond to any e-mails, messages, or any other form of communication. The original 2 papers were main parts of my dissertation and are still stuck as there is a lot of heavy lifting such as rewriting, revisions, etc. that I need to do alone. I am working on them, but I do not feel comfortable anymore about having someone in the paper who doesn't even reply.  

At this point, I am not sure on what to do. The very straightforward answer will be to drop X from the papers, but is that correct? or should I just leave the 2 papers and move on into new things?, which may also mean to "loose" the data.

Added: 
Thank you for your answers. I agree that gifting authorships is a wrong practice, although it is often difficult to convey to a group of authors who have very close friendship ties among them (that's what happened with the co-author who finally included X in the project). The main question now is whether I stop working in the existing 2 papers and put them in the drawer. They are interesting projects but given that they need significant work and X is gone (X and I knew this and that's why we decided to work together to "share" the load), it seems more practical and rational for me to move into something new (not using that data) with different people who are motivated to work. 

On the more subjective side, X has gone around saying not very nice things about me, and this has somehow affected the professional and personal relationships that I had with others. Given that, I feel even less motivated to work on these 2 projects and "give free work" to X. Is it worth to give up the 2 projects? At this point I am still confused and this has generated a lot of stress both personally and professionally.
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.