I cheated on my Girlfriend..Help?!?

So i've been with my Girlfriend for 11 months now, and everything has been so lovely up until now! The other day i went to a nightclub, out of my face, kissed a girl. The other night i told my partner what happend, obv she wasent happy, very upset as anyone would. She says she still loves me etc. But i need a 2nd Opinion, what do i do? What can i do? Please help.