I met a Chinese colleague in a conference, where we identified a research topic of common interest. So, we agreed on collaborating on a project and started exchanging some emails about the project, where we came up with a clearly defined project and preliminary results (including R codes and statistical models). This happened in the course of around 3 months after he went back to his country.
Then, he started taking long time to reply to my emails, claiming he had internet access issues until one day (at around 6 months after we met) he stopped replying. So, I just thought he was not interested in the paper anymore. However, around 2 years later, I saw the paper published in a top biostatistical journal. At first, I was dumbfounded to see it was exactly the same idea, same formulation, just with the remaining bits and pieces completed. Two more authors were included in that paper. I emailed my colleague to "check if he wanted to continue our collaboration" but got no reply anymore.
I went on a rollercoaster of emotions, thinking of emailing the Editors (I have emails and drafts and code), but then I decided to leave it to Higher Powers in Life.
My question is, in general, what is the Ethical thing to do when you find your colleague publishes a paper on something you contributed, not only to formulate, but also to develop.