Crush on a girl at work

I’ve been with my boyfriend 6 years, and three years into the relationship I realised I was bisexual, but I haven’t told anyone and I plan on not doing so.
I started a new job a few months back and I saw this girl in one of the other departments and I instantly was attracted to her. She’s quite reserved, quiet, but also really cool and clever and I have an enormous crush on her. Over the last few months it’s intensified and she’s all I think about. Every day I get excited to see her, and I get really nervous and shy when she’s around. I haven’t really spoken to her much besides goodbye and hello when she walks in the door because she’s on a different department. I have added her on social media’s but I’m reluctant to message her because a) I have a boyfriend and b) I’m too shy.

She hasn’t been at work the past few weeks because she’s been working at home and I’m not sure when she’ll be back at the office but I’m starting to really miss her, and her absence is making me like her even more. She is literally on my mind constantly and I feel so dumb because I haven’t spoken to her, and I’m in a relationship with a man. I really don’t know what to do. I would literally change departments just so I can be around her more and talk to her even that little bit more. I really wish I was single and I could attempt to pursue her, she’s literal perfection. I am feeling really lost, frustrated and confused and I really could do with some guidance. I feel like a teenager all over again!