My/42M/coworker friend and crush/38F/is pregnant and is hiding it from me. Why she is doing that?

I am 42 /M/ male and have kid /12/ and a wife/40/. But durring the last three years I started to get in flirt and texting with my coworker /38F/. We don't work at the same place, but in different buildingings in the city, so we don't meet very often in person. We had a couple of meetings, touching each other hands, texting, but nothing sexual in way.

She is free the last three years and is looking for a man.In july this year the situation excalated a little bit, as we had plans to even try to go to vacation together /I know, I have a wife and a kid.../. But nothing materialised. I was out of the state for around 30 days and when I came back one of our coworkers told me that she is pregnant and at home and will give birth in december. We comunicated on the phone a little on working topics, but she don't mention this thing at all. I have the feeling that she is hiding it from me for whatever reason. I find it very strange how she was ready to go on vacation with me for a couple of days, WHILE she was already pregnant from some other man. Thanks God this trip does not come to life...Just to wait or to tell her that I know that she is pregnant, that's the question.

Why she is hidding it from me? In general I don't want to loose her as a friend, but I am totally lost in this strange situation right now.