Although it could be possible for you to transmit the cold sore virus to your girlfriend through sharing the same drink, it is unlikely that the symptoms that you refer to were caused by the Herpes virus. 

The main reason for this is that the herpes virus normally has an incubation period (time before any symptoms show) of approximately 2 - 20 days.  So, if you and your partner both started feeling unwell immediately it is more likely to be caused by another culprit, such as a flu virus or bacteria. 

To find out for sure what is affecting you please see a Doctor for guidance as soon as possible.

Local Clinics: http://www.herpes-coldsores.com/support/std_clinics.htm

It is also important that you refrain from having any contact with the area when you have an active cold sore.  You should avoid contact as soon as you notice signs or symptoms (such as itching or tingling), while there is a sore present and at least a week after the outbreak has completely healed.  This is because herpes and cold sores can be spread even when there are no symptoms and these are the most high risk times.

To get informed on how to prevent transmission this article will be helpful:

• Facts about Spreading and Preventing Herpes