Stealing a girlfriend from another guy?

[Gary]

Okay internet, I've been and contributed to Yahoo answers before now give me something back

For arguments sake, I'm "Gary", I'm 18 and in my final year of school in the UK. I am insanely interested in this girl; let’s call her "Emily". I left school for a year and came back for 6th form and was re-entered into a year group that was not my own so I hardly knew anyone there. For over a year now Emily and I have been chatting and texting and getting very close.
Emily has been in a relationship with her boyfriend "Iain" for about 2 years now. Now I feel I've known her my whole life and she's exactly what I'm looking for; smart, beautiful, good sense of humour, same views, interested in a serious long-term relationship etc. When her and Iain have arguments she always texts me and tells me and wants me to comfort her to which about 50% of the time I do, but I can’t let myself appear too "comforting" to avoid entering the friend zone.
Last week I had had a few too many drinks and I called her and left some voicemails for her to find. I announced to her (I think) that I was crazy about her and she deserves better than to be treated the way Iain treats her sometimes and that with me she would never get that treatment. The next day she asked me what I said and I told her I didn't (even though I did). [This is where it gets tricky] - see, I know I like her, and she knows I like her, but she doesn't know that I know she knows I like her (still with me?).
Ok so now I have fully announced my feelings for her and I let her take it which way she wanted and stopped talking to her for a few days (not in an arrogant way, but to see her reaction). Then she started asking me what I remembered from that night and was interrogating me about it to find out (I assume) if what I said was true (which absolutely was) but the only way for me to play this (I think) is for me to tell her I didn't know about it.
It's been 10 days now and we're completely talking and texting loads now. She wants to spend more and more time with me and she's shared more private information with me (and so have I to her) and I get the feeling she wants me more involved in her life. I'm getting the impression from this girl that she wants me to be in her life more and more after hearing what I had to say about her. But the thing is there have been many guys before me that have done the same and she's turned down to be with "Iain".
I am a year older than her as she's 17 and she sees me as much more mature than anyone in her own year or her boyfriend's year (Iain is 16 and is in the year below her). She's been with him for over 2 years and he's been to hospital for a stubborn leg injury and they are extremely involved as a couple - I don't know how "far" they've been yet but I know she's not a slut.
Iain has tried to add me on Facebook and Twitter both of which I've denied and not followed back and I've never spoken directly to him (nor do I ever want to) but I get the impression that he wants to talk to me. He's a whole 2 years my junior and he seems like a nice enough guy from the outside but he's treated her badly before.
Last week at a Halloween party she phoned me 5 times and after she got kicked out of the bar was texting me while walking home alone. I texted her until she got all the way home and showed her how much I cared about her and that Iain should have been there to walk her home and make sure she was completely safe - which was when she told me he was annoyed with her and they had had a row.
I'm getting the inference that this girl likes me in a way that she hasn't liked other guys before. Iain, I'm sure, has treated her very well in the past but as soon as he drops the ball is the moment he doesn't deserve a fantastic girl like Emily any more. I have so much more to offer her than him and so much to give.
I am absolutely crazy about this girl and cannot stop thinking about her. It's the kind of feeling that you don’t just want to have sex with her; you want to care for her and be there for her and for her to be a massive part in your life.
Here are my questions:
Should I try to break them up?
Would breaking them up make me a terrible person?
If I should try to, how would I go about it?
Does it sound to you like I'm in the friend zone?
Should I tell her that I remember calling her that night and everything was true that I said?
Thank you so much for anyone who has listened and/or read this far - I'm sure there are many questions like this but there are none that are directly applicable to the nature of my circumstance.
Once again, Thank You - and I look forward to reading the answers.

[Owl.]

No, don't try to break them up, it's just gonna look bad on your part. She might not forgive you if you do. Yes, you should tell her that you do,remember what was said that night, & that you meant all of it, but beware that you telling her that might change the kind of relationship you & her have at the moment. If she seems so very dedicated to her boyfriend, know that she might not break up with him for you. Now that you know what is at risk, you have to ask yourself, are you willing to take that risk or let it play out, meaning denying what you told her in the voicemail & just letting time pass & wait for her to break up with her boyfriend on her own terms. Good luck.