Why would she keep her engagement a secret?

I've been hanging out with this girl for about the past month. We haven't actually hung out more than once every 2 weeks due to our busy lifestyles but we would text back and forth about twice a week for the last couple of months. When we would get together, we would go to a coffee shop and just talk. Yesterday, we went to this coffee house and I planned to pop the question and ask her out today. I got input from all my female friends and they told me to definitely go for it before it was too late. So everything was going fine and I overheard her say my name on the phone to one of her girl friends on the telephone (very good sign). A couple of hours later a guy came in, gave her a huge kiss on the cheek, and told her that he had to tell her something. They walked away for a second and came back and he had his arm around her and when he left, she awkwardly told me "that was my boyfriend. I never mentioned him because I barely see him. We've been together for 8 months now and we're engaged." So whats going on? After knowing her for so long, she never once alluded/mentioned him like she did her exes. What is going on?

Same reason why taken/married guys won't say they have a partner.......incase it puts you off.

Hi,
Firstly, I'm so sorry to hear that you've been messed around. It sounds to me like she's been keeping her options open and wanted to keep your hopes up that you could be more than just friends at some point and this is why she didn't mention the boyfriend/fiance - which in my opion is a mean trick. My guess is that she's not getting the attention she wants from her boyfriend/fiance and was filling the gaps with you. I think she's been deliberately deceptive and I don't know about you, but I don't tolerate that from my friends.
Her motive for doing so ? Who knows for certain. If I'm being charitable, she sounds mixed up, not getting what she wants from this guy who seems to have a hold on her and is confused about what she wants from you. If I'm being uncharitable, she's messing you around and using you. Either way, she's not been honest and she's not considered your feelings.
Where to go from here...move on and find a girl who's available to give you all you want and deserve. Sounds harsh and I'm guessing you'll miss her but I think you'll be heading for heartache if you carry on with her.
Hope that helps,
Lizzie

Walk away. Its not your place to interfere with such things

I was engaged once. To a woman who behaved like this. She often failed to mention to people that we were engaged. Particularly to people who showed an interest in her. Obviously, it didn't last. I left her. Later she confessed to me that she never wanted to get married in the first place.

This girl didn't tell you she was engaged because she didn't want to. That being said, you shouldn't take it upon yourself to break up this relationship. That will probably happen without your help, and it's not a situation that will be fun to get involved in.

The only times I ever failed to mention that I am in a relationship were on purpose. I wanted attention and I knew that the way to get it was by appearing single. It's a stupid immature trick that represents how inexperienced and socially clueless some people can be. If you are proud to be with your significant other, you tell everyone, like I do now with my current boyfriend.

I'm confrontational and I tend to call people out on their sh*t, but not in a mean or spiteful way. I like directness and I expect the same from the people I keep in my life. It'd probably be best for you to step back from this. Your feelings aren't going to dissipate anytime soon and she seems to be enjoying having you around. She's borderline cheating right now, in my opinion. Her purposeful deception combined with her frequent outings with you point to that. And she never sees her fiance? I wouldn't be marrying someone that frequented my life so little.

My gf may have to hide our [hypothetical] engagement for employment purposes. In her country, employers may discriminate against. If they knew that she was engaged to a foreigner, they would not hire her, simply because she could quit and leave the country.

This woman you've described sounds a bit fishy to me though. I would stay away.