IS GIVING ORAL TO SOMEONE ELSE CHEATING?

so i found out yday through a friend that my girlfriend gave oral to a couple of guys at a party.
its so angry and i confronted her about it, and she told me the reason she didnt tell me about it
was because she didnt think it was cheeating...then she went ahead and told me i was overreacting and asked me if she kissed her brother on the cheek is that considered cheating? since theres no physical intercourse. I'm pretty sure its cheating but want to know what you guys think