I've cheated! What shall i do??????????????????

Last weekedn i went out with my bro's and had an incredible night, i was in the mood for celebrating as just found out my girlfriend is pregnant! So as a night out the boys offered to trake me out adn buy me drinks. Before i went out however i had a huge disagreement with my girlfriend. She thought that i had no right to go out and drink as she couldnt and apparently i should have to stay in and look after her for the next nine months and be at her beck and call the whole time throughout the preganacy. I explained my dissapproval but she wouldnt have it. I told her to invite her friends round and have a girly night and i would go out on the town with the lads, She was going crazy! She was so angry but i couldnt take anymorfe so i went out and i had an amazing itme. However as the evening progressed, i met a girl she was amazing and everything i had ever dreamed of. I was so drunk i we kissed! I went back to hers and we had the best night ever! I then went home to my girlfriend in the morning, who was then mad that i drank so much, she is still unhapp with me but what do i do! I feel so bad but was this bought on herself? What should i do! PLEASE HELP