Why would a girl keep hiding her boyfriend?

[Anonymous]

We work together with this girl for a year. It seems like she shows me plenty signs of attraction. She does have a boyfriend as I found out and she mentioned him to another co-worker but she hides him for me. I even tried prying and finding out who she went on vacation with and she said friends when she went with him.

What does this mean?

[Avicenna]

Its weird. Hard to say for sure.