Honestly, if you're comfortable going out and talking to mutliple girls at a time, then do it.
I guarantee you these women who are online getting 50 emails a day from guys trying to get a date with them aren't exactly ignoring all of them either.
She did it for kicks at the expense of what she knew was a good potential relationship... I didn't have a problem meeting and dating (in the short-term) several women, and had no problem with them doing the same. I would have been happy for her, as well, though of course disappointed for myself. If someone else made a better match for either of us, we would have and should have gone with that other person.
One woman seemed to be ideal for me (and indeed became my long-term g/f and wife), but she wasn't ready to commit since she needed some basis for trusting her choices after a very bad relationship. Everyone else just made us each look that much better, so eventually she was able to make a good decision based on the knowledge she gained. However, once you become exclusive, the search for and dating of others stops while the relationship lasts.
Next time you are interested in a woman and you want her all for your own, let her know before you leave town.
Everyone has their own ideas about when it's appropriate to become exclusive.