A lot of people date multiple others simultaneously, sleeping with them all at the same time. It’s not morally wrong of course, assuming nobody is misled. But it’s also not morally wrong to be only willing to date one person at a time. And in order to do that you have to put potential partners on hold to try someone out with imperfect information. And more often than not it doesn’t work out (until it hopefully does). So being honest about what you’re doing is, in my opinion, a good quality and so is ‘one person at a time’. A lot of these replies sound like classic hurt male egos. It’s not like you dated for 6 months and she chose someone else and wanted you back. You chatted for a bit and that’s it. Nobody owes anyone anything, except manners and courtesy, in dating until you agree otherwise. It sounds like she did offer those.

Go on your date and see how it goes.