It seems like she's in her experience phase. Are you guys in uni/college? I understand that phase, and unfortunately, I have been guilty of similar behavior also. It is a bit selfish for sure, and I felt pretty awful afterward.

I hope in time she understands what she kinda did to you.

This being said, lose the attitude of "girls i date, always have another guy" approach to life. It's self loathing, desperate and people can smell that shit on you from a mile away. Especially in the dating scene. Go into all dates with 0 expectations. The only thing you are promised on a date is an interaction with another person for a short period of time. Any assumptions or expectations met outside that are dumb. You can have intentions, and that's fine, but don't expect love, sex after a first date. Not that it's impossible, but expecting it is also dumb.