Since you have spent so much time and effort on your research, you should definitely write your manuscript and try to publish it. While it is true that most journals are not open to publishing negative results, one cannot deny that publishing negative results is also important for the progress of science. Negative findings can provide meaningful insights and should be published.
If negative results are published, unnecessary replication of work can be avoided. Researchers would know what doesn't work and would not spend time, effort, and resources on a hypothesis that someone has already worked on and found to be incorrect. Also, negative results can make way for positive results. Based on the negative findings, researchers can make informed decisions and try out other methods that might yield confirmatory results. Even Einstein's theory of relativity was based on the negative results of a series of experiments conducted by scientists before him.
I do agree that the current publication system is flawed and there's a strong bias against publishing negative results, but it's up to scientists like you to change that mindset. In fact, the scientific community does recognize this problem and many of them are trying to rectify it. Thus, there are some journals such as Journal of Negative Results in Biomedicine, PLOS ONE, and The All Results Journals that encourage researchers to publish negative results. You could consider submitting your paper to one of these journals.
You might also be interested in reading the following articles:
- PLOS ONE's new collection to report negative, null, and inconclusive results
- Amgen to publish negative results to improve science's self-correcting nature
- How publishing replication studies and negative results helps science