I first commend you for looking for help and advice. While you probably should have started thinking about these things earlier, it's not too late because you still have a girlfriend that loves you. I think. Does she sound distant as well?
It sounds like you have lost the excitement you have in your relationship. Why is that? Is it because you are comfortable and don't feel like she is going anywhere, albeit bored? Is the sex life dwindling? There has to be some reasons here and if you can answer them honestly with yourself, you are on the way to recovery.
I think it shows you care for your girlfriend and it has to be weighing on you to have this confusion on your conscience. Take it easy with the other girl for now before you figure things out. Talk and communicate with your girlfriend when you think you have a handle on things. You don't need to tell her that you like somebody else, you need to ask her how she feels about the relationship and any suggestions you can use to jump start things a bit.
That's if you want to keep what you have right now.
Waking up next to a beautiful girl,
Step outside and say hello to my beautiful world.