Co Worker crush has started ignoring me. Should i ask why?

For reference

Me - 25 - Single
Her - 25 - Boyfriend of 7 years
Other guy - 34 - Married, kid
She is in our group of friends in work (Me, 2 other guys and her)

So, there is this girl i work with. I've had a major crush on her for a while. We have been talking via Skype in the office for the last 6-8 months. At first the conversations were really long and in depth. We would talk all day. But now it's changing. In the last few months she never ever initiates a conversation with me, i always do it. Were as before she would always start talking to me. I still talk to her and she still replies and is friendly, but the conversations are feeling more forced and takes longer to reply.

The hardest part about all of this is that she is now talking to one of my friends from in work. From where i sit i can see her in front of me and him to my left. They are talking every day, all day. Like we used to. Sometimes we will be having a conversation and she won't reply, i look up and i see her smiling, typing furiously. Then i see my friend to the left gets a message and i can hear them typing to each other. So she will just forget about our conversation and talk to him all day. It's making me really jealous and sad, we catch each others eyes sometime and i find myself hoping she'll remember we were having a conversation and reply, but she never does, just keeps messaging him. I'm sure it is innocent and friendly but i'm getting so jealous i can't deal. I just keep wondering, why has she stopped messaging me like that and seems to have an infinite amount of stuff to talk to him about.

We still talk but it's not like it used to be, a few times i've tried not speaking to her for a day or 2 in the hopes she will message me first. We also used to talk via facebook, again she would initiate a conversation, tag me in things, not anymore.

So my question is, what should i do? I wouldn't try anything since she is in a relationship. But i really like talking to her, but the way it's going i'm getting too hurt watching her ignore me for him. My mood is being dictated by the quality of conversation we have. So i was thinking about completely stop initiating conversations and only talk to her in person when we run into each other. But i have the fear if i stop talking to her she will just forget about me and that will be it.

I am thinking about casually asking why she is being quiet. Is this a good idea or will it just make things awkward? At this point, i just want to know what happened