Am I confusing myself with my emotions? Should I walk away?

I have a friend who I really identify with in terms of personality. We work together and also study at the same institution. She is a very honest person and although a little insecure, she is one of those few people who try to help others without any kind of malice or personal interest.
However, she is already dating someone else, and although I enjoy her company, it leaves me a little down sometimes. Even though I know it's not a very healthy thing, I often find myself trying to get closer to her, whether by going to events, helping with work tasks or offering help with studies.
I honestly feel very lonely lately, not only when it comes to romantic relationships, but also when it comes to friendships, and maybe I'm confusing the two things. Still, she's one of the very few people I feel comfortable being truly honest with.

What are your opinions? Am I really mixing my emotions? Should I try to walk away? Any advice?
Am I confusing myself with my emotions? Should I walk away?
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