What is cheating exactly? (Flirting,Kissing,Sleeping with someone)

Everyone has different opinions on that and well my fianceé kissed a girl on her cheek yesterday but like grabbed her and kissed her whole cheek over and over again and she was like recording that and put it on snapchat. I was like really hurt when I saw that I mean they didnt kiss any other way but i dont know I felt so hurt and he returned back home like a few hours later and I know he loves me and he really hates cheaters but honestly I feel like I've been cheated on. He left for this Halloween party and I really wanted him to go there since he was with me ever since we found out I was pregnant but he probably didnt even notice she recorded it and that I saw it but is this cheating? I'm like really confused and hurt I dont know what to do.