Gf cheated and sees nothing wrong with it.

Problem/Goal: gf kissed someone and sees nothing wrong with it Context: hi bear with me first time posting so yun nga happened a few months back but still its bugging me pa so eto na nga gf kissed a guy na friend niya sa inuman then kwinento sa akin nung best friend niya that time yung nangyari so i cried cause its the first time i gey cheated on then yun nung nasabi na ng bestfriend niya na nakwento niya na sa akin she came clean tsaka niya lang sinabi take note ang sabi nung best friend niya sa akin is sabi ni gf is she would take that to her grave so hindi niya talaga dapat sasabihin kaso yung best friend niya is friend ko din so i guess best friend felt bad for me? And then ang kwento niya is lasing daw sila and bigla daw siya kiniss nung lalaki but she kissed back so yeah and added note lang sinabi na sa akin ni gf na yung guy is umamin sa kanya na she liked her and then yun when i knew na the guy was with them i already told her na i wasnt comfortable with her being with the guy lalo na at inuman pa but she pushed ang sabi niya dont worry so yeah i trusted her kasi sabi niya naman eh then yun na nga after a few months we were playing this card game with friends and the card said "did you ever cheat on your partner?" And then she just said no so i just looked at her and sabi niya hindi naman daw considered na cheating yung ginawa niya so i was like "huh?" And i dont want to embarass her in front of friends so i just kept my mouth shut na lang and everytime i bring it up or you know talk about it ng maayos she just gets mad and ako naman i wont talk about it na so yeah yun lang all im asking is. Is it really cheating yung ginawa niya or am i just overexxagerrating things? What should i do? Need advice lang kasi im lost na i dont know what to do and it feels like i might not fully trust her again kasi she doesnt even see the wrong in what she did so yun lang hehe sorry napahaba na yung post.