How to keep going on without appreciation

So, there is this big project where we have partnership with a another big company and we have to deliver a product/model to them. I am the key ground level person working on the project. The project is having very very strict deadlines where we are trying to make something that our partner company made in 1.5 years and then thought to scrap it and take from us where they expect us to make something like they did in just matter of 2-3 months. This project is being also tracked by company top levels like CEO and president, so very hot project. Now this is the background, we had kind of completed the project and we presented it to the MD owning this, and he scraped whatever we did saying this is not enough. (despite he had agreed and knew what we were working from weeks) Now we had to restart much of the things from scratch with even less time to accomplish. I have been slogging and over working on weekends and holidays as well as stretching till 4am in the morning. Every meeting, the discussions are inconclusive and every potential scenarios is added to be worked on rather than finalising. MD doesn't tell what he wants but keeps on saying NO to everything we say. Now recently, he found one of the scenarios/stream of project which we had not optimised and stated this that this can be optimized if we take that route or path while finalising. Now rather than appreciating for once that whatever large set of simulations/work we have done, which was kind of impossible in the given time, he just wrote a very nasty message saying that he feels uncomfortable and WE ARE NOT DOING ENOUGH. Now, reading this message, i was kind of talen aback. I now feel less motivated to work on this project and it takes me a hard time pushing myself to get on desk and work, which i have to given the importance.

Earlier, it wasn't the case, despite me going overdrive, i kind of liked and took it as a task in my responsibility. I didn't had to push myself to get on desk on weekends and burn the midnight oil daily.

If anyone can help me figure this out and kind of give me some examples from their experience, it can help. Me explain myself to ignore it and still keep on the hard work.

I don't want to loose at this level, just because i lost enthusiasm just because of a nasty comment or feedback, which i totally don't agree as MD himself doesn't know many things going on on-ground.