should i tell a girl i like her, but has a boyfriend?

Okay so I have known this girl for about 2 years and within the last year or so we have become really close friends. We do things together like a couples would (movies, hanging out etc) but have never at anytime been intimate. Also there hasn't been a day that we haven't spoken on the phone to each other at least 2-5 hours a night as we are both night owls. We are brutally honest with each other and no subject is taboo. She makes no hiding the fact she has a bf and has spoken about him positively and negatively but we do speak of him and relationships from time to time.

There is a significant age difference between us as I am 10 years older than her. She is however very mature for her age. We do work together which is what I might be a factor for holding back.

Now I haven't had feelings for her in the past but have just recently. She recently came to the realization that she shouldn't be hanging out with a guy on her own while she has a bf. She came to this conclusion as she had given her bf a hard time over a similar situation. However the occasional movie or dinner has not stopped. Also our all night phone calls have definitely not stopped as it has now become routine. But this is when I realized that I like this girl cause that part of our relationship was kinda taken away.

She has often spoken of that age does not make a difference in relationships as her parents are 15yrs apart and as my father's second marriage was the same.

I will add the fact that I am recently divorced myself with 2 children. She had helped me through that dark time but at anytime these feelings did not arise.

She has been with the kids on a family day company outing and she is fantastic with them. My daughter is very shy around ppl and there has been only 3 ppl she has ever been able to open up with so quickly. This girl is one of them and the chemistry between them is amazing.

My dilemma is if I should tell her I like her and risk the friendship I already have. The thing is I am willing to wait for her whether there is a future with us or not. I am afraid if I do tell her she will become distant and eventually no longer be friends.

Please help. Be as brutally honest as you can be. I am looking for advice and hopefully I can come to a conclusion about it.