If a guy is lonely enough, he'll sleep with just about anybody. It's not like he was interacting with any other females. It's really not that unbelievable.

All of you are apparently oblivious to the fact that the actress is married to the writer/director of this movie, that negates everything you think about the appropriateness of her playing Nina.
Lou

Really!? She's pretty hot!

Inspect face first then drill, hard. Repeat.

Inspect face first then drill, hard. Repeat.

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Would agree, except that Bloom is a Norman Bates-type psycho, who would naturally go for a much older woman.

Eye of the beholder, yo! (I myself find Rene pleasing to the eye).
And come on, even though his interest in her was clearly more than mere physical attraction, it's fair to say that SHE was too good for him.
You want something corny? You got it!

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I think his reasons for pursuing her went beyond mere physical attraction, but regardless of Bloom's motives, I found her quite attractive.
Ghosts and lovers, they will haunt you for a while

Should replaced by Julianne Moore. She was beautiful, but wasn't something for him.
There's something wrong with Esther.

Not usually a women 30 years older.

Doesn't surprise me at all that he might want to have sex with her. Guys are like that. They say they'd "never tap that." But they would.

Talk to your buds and co workers and inquire what makes them wanna hook up. No one I ever met on TV or in real life said, "Hey I'd like to tap that. Her world view is in sync with mine." Maybe a little later it matters, but as we see, it turns out the two had a lot in common after all.

She is his access point, a tool for getting inside the business and his hooks into all her contacts.
Also, the movie isn't to be taken too literally. She represents the viewing public, who knows it's wrong but can't resist her voyeuristic need for what he's peddling. He represents today's media, unscrupulous. Having him beep her is well, it's simply fitting, in a symbolic way.
Besides, do you really presume to know what would attract someone like Lou?