In search of dating advice!

Ok, new dating type question. I am now facing a point where one of my online matches has definite potential, so when do I stop talking to my other matches? This is a new dilema for me... I've never been matched with someone who had ACTUAL potential, you know? I've done the first date with some, but after that, it's always fallen flat. This one could go further, so when do I end it with the others? Not that I'm doing anything more than emailing, but when does it end? Ok, there are no more ways to ask this question, so I'm leaving it to you. Thanks!