Insulating Yourself from this Situation I don’t have any secret on preventing this situation from happening.
It happened to me more than once (twice that I can remember although I know it happened more often than that).
It doesn’t mean he’s lost all interest in you…more likely he has found something that interests him just as much but is more accessible (closer in this case) to pursue.
Responding to This Situation All that being said, I think it’s very reasonable for you to reach out to him. That is, I would just come out and say “Why did you stop emailing me?!
When I was excited to talk to a woman I could barely wait to write my next email and actually had to force myself to pause sometimes. In this case, I would think it’s unlikely that you did something wrong. However, once the long emails start I believe the (unspoken) social contract has basically been signed and continuing to write long emails it totally acceptable.