Ok, I have a girlfriend... But recently I started to like this coworker of mine. We chat often and sometimes we go out together (as friends). I think I really like her, but I also still like my girlfriend... 

My girlfriend knows that we go out sometimes (just grabbing a drink) and that I chat with her often. She doesn't know I like her too... 

I don't want to choose between them, I love them both equally... 

Any advice?