I am one month away from finishing my dissertation. I did not receive much guidance from my supervisor, so I asked a co-supervisor to join my project about two years after I started (with still two years left). In these two years I think I had 5 or 6 meetings with him, which is not too often, but his feedback in these moments was always very valuable. Moreover, when my relation with my supervisor deteriorated, he was there to 'protect' me. I am pretty sure I would not still be working as a graduate student otherwise.
He now points these things out to me in quite an angry way via email and argues that I have not provided him with enough output to justify the time he has spend on me. We currently have one paper together that is under review. I have no idea how to provide more output for him because we have no other papers together. I have only one month left in my current contract so I don't want to start a new paper. I can put his name on another paper that's currently under review but that doesn't feel right since he did not contribute to this paper.
Right now I feel very stressed about this and I have no idea what to do. I cannot afford to have a bad relationship with my co-supervisor right before I wish to submit my dissertation but I also feel this guilt trip is not fair. What do you think? Do you see a solution? Thanks for your advice!