I like this girl, but I think my friend does too

So this gorgeous girl joins our social group, and I'm immediately smitten. She's the complete package - smart, funny, exciting, musical and beautiful. The phrase 'marriage material' would not be inappropriate.

She's living with two of my friends, Friend A, who's gay, and Friend B, who's not but as far as I know has never had a girlfriend, or much interest in girls. He's rather a geek and (I'm ashamed to admit) I have never thought of him as being interested in relationships - he's certainly never shown any inclination to be.

I was in a 2-month-old relationship (my first for 3 years) that was going nowhere, and we both knew it. We simultaneously broke it off - very adult, no hard feelings - and I give it a couple of weeks before inviting this new girl over for dinner.

We have a good time, drink plenty of wine between us and make sushi. We talk about our past relationships (she's a year out of a long-term one) and both say we're ready for something new.

We continue to hang out as part of a group and at work, but there's no real chance to talk to her alone, you know?

During this time I become aware that Friend C fancies her. I consider myself a better match for her than Friend C and I'm sure we're closer, so I decide to try to say something. I buy theatre tickets and we have a fun night, but there wasn't a chance to properly ask her out. Beforehand we were with a bunch of people in a pub, and afterwards we just went home. I hate myself for not being brave and saying something, but I've always been like his with girls. I hate the thought that I've missed my chance.

Now, this afternoon I was over at Friends A and B's house playing games with a couple of other people. She comes home, and then after a while goes to the pub with Friend B. At 4 in the afternoon. They're laughing together. They invite us, but the rest of us feel like we'd be interrupting.

I feel like someone's shot me in the stomach. I had no idea, bit now I think about it I can see evidence that Friend B does like her. Or maybe I'm imagining it. I'm certainly not sure whether she likes me or not, but I would have given myself a good chance before. Now all I can think about is how my weird, slightly-strange-but-once-you-get-used-to-him-pretty-fun Friend B and herare going to get together and live happily ever after and I feel physically sick. I feel like I've let the opportunity of a lifetime go past.

And I am so sick of being single. That recent thing didn't really count and I KNOW this could work if she was amenable. I don't know whether to back off and let my friend try for his happiness, or to say something to her and potentially have something great happen to me, or make things awkward for them, or both.

Has anyone been in a similar situation? I don't have experience of, for want of a better phrase, screwing over a friend to try to get a girl. But as I say, this girl is really, really special and I'm not exaggerating here.

Sorry this is rambling, needed to talk to someone but can't really turn to any if my usual friends because everyone involved is in the same social group. I've been worrying and worrying a out this for hours and it's brought on my anxiety and depression in a big way. I drove a bit this evening and mildly contemplated having a minor car accident so I wouldn't have to think about all this for a while.

Any words of advice/comfort?

(Sorry if that sounds needy, feeling a bit vulnerable now)