The girl on the train, with the other man, is just a girl; she's human, not an angel, but she is as beautiful as an angel describes the singer:
I saw an angel.
Of that I'm sure.
She smiled at me on the subway.
She was with another man.
Below, the singer is referring to a real angel, one that planned for the singer to see the beautiful girl on the train. The real angel is described as a matchmaker:
There must be an angel with a smile on her face,
When she thought up that I should be with you.
But it's time to face the truth,
I will never be with you.Re: Does "my life is brilliant" mean 'my life is smart', 'my life is great' or 'my life is cool'?
There are several meanings, actually; wonderful, splendid, magnificent; vivid. I like the last one, vivid, because the singer talks about being "high"; the girl's beauty alters his perception, puts things into a clearer perspective. But that's just my interpretation, one interpretation among many. I am sure you have your own.