I sounds to me like she's getting bored of you. I don't think she's seeing anyone else, but I think she might feel like you're being clingy, or rushing things. If you love her so much, then try doing something you know she loves to do. Maybe try and invite some of yours and her friends too, because she might be feeling awkward with just the two of you. Maybe try and talk to her and ask her what she wants to do, and if you're worried about another guy being in the picture, you need to be careful how you go about it. Don't snoop, but by asking her straight up, she would think you don't trust her. You could lose her that way.
I don't think she's two timing you, but she's most likely bored. So try changing it up a bit. Don't let her lead you on though, I don't know you but I would hate for you to get hurt.