Many props to Meryl. That's devotion to someone loved.
How About That?

I didn't know they were a couple. Here's a link to a very good article about them.
http://nypost.com/2016/04/23/the-tragic-romance-that-shaped-meryl-streeps-life/

They were together 7 years

I believe they were together about 18 months before he died. They were engaged and she lived in his apartment. She was shocked when he died. Maybe because it came sooner than expected or because he was somewhat high functioning up to the end. She stopped acting to be with him in the hospital. When he died, she was asked to leave his apartment and moved into a place whose owner was out of the country that her brother knew. When the owner came back, they dated, fell in love and got married. She really is something special.
"instant gratification takes too long"

she didn't meet him on the set of The Deer Hunter, they were in a play together in New York, but he was very famous already and they fell in love. they were already engaged when they were both cast in The Deer Hunter.

That's quite possible, but I've never heard that she mentioned John Cazale in her remarks.
There is, however, a wonderful AFI clip at youtube in which James Wood talks about being with Meryl after Cazale (who is not mentioned by name) passed away, when she met Don Gummer. Meryl and Don married within months of their meeting and seem to have a very healthy, enduring commitment to each other. Here's the clip:

I know this is an out-of-date topic, but I just saw the video of her speech on youtube.com (I have a lot of free time). It looked edited. They probably had to cut some parts of the ceremony out of the telecast for time reasons. If an article said she thanked him, she probably did.

I saw the AFI tribute, and she didn't thank him. The only people she thanked who, as she said 'couldn't be here because they're in heaven' were her parents.
He was mentioned by James Woods though, in his speech, briefly, and Meryl looked really sad. I can definitely understand why she doesn't speak about him publicly.
I just realized you can see completely through my dress!
~
Meryl Streep

Well, pushcrush, as I said I didn't saw the show, so I can't be 100% sure of that, but I read the press release of the event and they said that, at some point during her speech, she thanked the people who wasn't there anymore but who counted a lot in her life and her career, including her parents and John Cazale. I will try to find some of them.

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That's not absolutely true. Meryl Streep and John Cazale met before filming the Deer Hunter. If I don't make any mistake, they met while doing a play in New York in 1976. I think it was Measure for Measure. At that time, Cazale was already a well known actor (the godfather, dog day afternoon), but meryl hadn't play in any movie. She graduated from the Yale School of drama in 1975, so she did that play shortly after that. I suppose cazale suggested meryl to cimino to play in the deer hunter. Meryl often say that cimino didn't know what to do with linda's character, so she had the freedom to construct that character by herself. I think she did great.
But you're true, meryl don't often mention cazale. I think that's because she's a very private person. I didn't see the AFI lifetime achievment award's show last year but she actually thanked him in her speech.

Streep met Cazale while filming his final film - The Deer Hunter - and they not only went out, they became engaged, too. Rumors have it that when the producers wanted to fire Cazale because of his illness, Streep stood by him and threatened to quit if he was fired. Cazale died shortly after the film was finished.
I often wonder why Streep never mentions Cazale, I suppose it must be a painful subject. Can't really blame her.
"Mmmm Unprocessed fish sticks."