Is that my fault that she likes me?

Ok I have a girlfriend and we are very happy and we been together for 2 years and I luv her. But there’s a girl I know for 5 years we used be in the same college and now we work at the same place I see her everyday. Now here is the problem she likes me her friends are my friends too and they been telling me that she is obsessed with me and that’s why she got the jab in my company & she never had a boyfriend in 5 years but I have never notice that. But now I have notice couple of thing like she doest leave the building till I leave, takes days off when I m off, text me everyday, always staying around me, staring at me all the time. Now I feel so stupid I luv my girlfriend but I don’t wanna loose my best friend either or heart her feeling. My gf don’t know about that but they know each other. My friends said that it’s my fault I was been way too close with her but I m like that with everyone. I did try to ignore her text couple of time but I don’t know why I feel bad. we never had any uality activity either. What should I do???? Is that my fault that she likes me???