Still get engaged?

First time here. My relationship started out great, as of recently it has gone a little sour. When it comes down to it, and i ask her why, (cause i have no idea sometimes why my girlfriend acts like she does) she tells me she wants to move forward with the relationship. I can totally understand where she comes from. We have been dated about 2.5 years. Not super long in my eyes (super long meaning the time when she should be like, "lets get married now or its over"), but long enough that i know we love each other and can be happily married.
well, thats the point we're at now. She says lets get married or its over. I have no problem getting married, and want to with her. Heres what i'm not sure about though. i have never lied to her. i have told her that i want to get married, and will ask her to marry me. however, she says she doesn't believe me. this hurts greatly as this is not the case. this came out a few weeks ago. all this time i have been researching and now buying an engagement ring. this is where my problem comes in. i feel that she should at least talk to me this whole time, but she hasn't been. we text here and there, but not really talking. i told her i am getting a good ring, and want to do it the right way. this is just taking some time to do. she didn't really like that idea i guess. so i asked her right then. she didn't answer, saying, she didn't think i meant it.
i just need some perspective. She will marry me. lots of her texts say she is getting fed up though. in my eyes, until i ask her, she should still be nice shouldn't she? maybe your thinking no. but in my head all i can think is, i'm working hard on getting this ring, and want her to be patient and believe me that i will ask her. and all i seem to get from her is coldness. this has been for the last few weeks. i don't want to be with a cold person. and to me it just feels like her not being nice to me is forcing me to ask her just so she is nice again.
i personally don't think getting engaged is necessarily signified by a ring. what i mean is, if i ask her, and she says yes, then we are gonna get married. i am getting a ring, its just not done yet. i say this because i feel that if i ask her again without a ring this time. she will still not think its real, and i'm not serious unless i have a ring. should that matter too. i feel like i am rushing it cuz i don't want to loose her, but the rings not done. i'm ready though.

Thanks.

I say that she isn't worth it, she is acting like she only wants you for things you can give her. She won't marry you unless you have a ring, she may think once she has the ring you''l get her anything. I don't think she loves you as much as she once did. I could be wrong but thats how i read what you wrote.

How can she even cut you out of her life, if she loves you? Sounds kinda weird.

This is a little manipulative, in MY opinion though. If someone did that to me, I would question them. If they love me, why are they being mean to me and cutting me out of their life?

Don't judge her yet though. Give her a chance and talk to her about this. If she doesn't even want to communicate with you, then you have a problem. Marriage depends on communication...

Yes exactly!

I have a pretty huge bias against bride-crazed ladies to begin with, so I apologise in advance... but, really? I think that if she is this anal about getting her ring and getting it within a certain timeframe, particularly if she is going to emotionally punish you, otherwise, there might be some deeper issues here. Have you ever asked her why she is so eager to be engaged? What exactly that symbolizes to her? I think that if you approach it with a genuine aire of curiosity, you might be able to gain some insight that makes this whole situation a little more illuminated for you. I know she says that it's about "advancing the relationship", but what exactly is the rush? I cannot see any logical reason why any emotionally stable woman would get so frantic about an engagement unless she had some ulterior concerns brewing.
Although one of your initial comments (cause i have no idea sometimes why my girlfriend acts like she does) leads me to believe that there is some antecedent knowledge to which we of the forum are not savvy.

Yeah, but if she insist to not tell you, then she is hiding something, and you need to just break it off with her if she does not tell you, that is just mean and hurtful.