Typically any holiday is spent with your partner (if possible, exceptions can be made in advance... "I'm sorry I can't spend fourth of July with you, I need to work on that day" for example)
Discuss limits, periodically confirm limits haven't changed. Maybe hanging out at a beach with a different potential partner is a limit. Maybe having dinner alone with a different potential partner is a limit. Maybe kissing is a limit. Maybe sex is a limit. Maybe the gender matters, if your partner is same gender as the other person may increase the limit(if your partner is a girl, she may not be ok with your kissing a girl but if fine with you kissing a guy for example). All these vary by partner.
Communicate... Why is she upset? Was it timing? Would what you did be ok next weekend for example? Was it the activity? If you saw a movie with your friend would that be ok?
I don't mean to be offensive about this one. Why did you leave your partner to spend time with another person? Did you not like spending time with your girlfriend? Did you prefer to be around your friend? Did you just need a break of the party but it's awkward to return to the party afterwards? Do you just not like that type of party and that's why you left?
All of these will influence your relationship. The biggest is going to be 3.... Communicate communicate communicate. Discuss these questions with your partner and you should have a better idea of what is acceptable and what isnt going forward.