Editorial Ethics and Respecting Respect

So here is the story:

After returning from a trip, I was talking on the phone with the editor of a magazine for which I occasionally write. We chatted about a number of ideas for his magazine, including one we both thought was interesting. I followed up with an email, to which he replied that the magazine was seriously considering the story idea we had discussed. He then asked me for more information.

I did my research and put out a HARO on the idea. I forwarded the relevant emails to him and reiterated my interest in doing the story. I heard nothing for a while. Then, yesterday, I opened the most recent issue of the magazine to find the exact same story idea written by the editor and based on the sources I had provided.

I emailed him and heard back this morning. His explanation was that another story fell through and he wrote the story quickly. He apologized and told me that since his magazine is a small niche market, I shouldn't have any trouble reselling the idea.

What do you suggest I do?