Would you class this as cheating?

OK. so i was at a party at the weekend and there was alot of drinking involved. i invited my girlfriend along so that she could meet all my friends. she got drunk really quickly and ended up passing out for the majority of the party. Obv, i was really embarassed by her behaviour because i was hoping she would make a good impression on my friends because She also got really emotional about everything and was speaking in a very obsessive and protective tone over me. She says i love you alot but we havent been going out for that long so i havent developed that feeling yet. I told her to go sleep it of but she just kept getting up and saying things like "oh ive ruined things between us" and "are we okay" and "i need you, dont leave me"...i was trying to enjoy the time with my friends at the party too but i was so angry and upset with her for being soo immature. By this time i had alot of drink in me..there was a mate's sister there and i could tell she was flirting with me. i reminded her that i had a girlfriend but she carried on being flirtacious and well,it was pretty hard to shift her off me..when no one else was about we were sitting next to each and she kissed me. i feel absolutely terrible but i was very drunk and upset ..i know drink should not be used as an excuse but im never like this and i wouldnt ever normally do anything on that scale..would this by classed as cheating?