Could someone shed some light on it? When did he marry? What was the marriage like? When was the divorce?

He married Denna, and I'm sure it wasn't long before Godfather Part II began. Denna was a disgrace though to Fredo, an embarassment as it was evident as the communion party. Their marriage wasn't the best and maybe the divorce took place when Fredo "drowned" in Lake Tahoe.

Presumably Fredo married Deanna in Nevada because he was single at the time he was shipped there following the Don's shooting. I don't know that they were divorced--she was still around at the time of the Tahoe attack.

I assume for several reasons that after the communion in Tahoe, she was sent out of the picture 1) When she was drunk and said "Never marry a whop...." and "You couldn't hit your momma!" The look on Mike's face was one of both embarrasment and disgust at the same time. 2) When mamma Corleone died, I don't recall seeing her at the wake. Also we can assume that Fredo had problems with her as in a deleted scene when they are arriving at the communion she belittles Fredo and at the same time disses Mike. I think that FFC shot these two scenes with the intention of showing the veiwer that Fredo was having his problems with his wife.


Don Cardi

Maybe these two took the place of Johnny and his second wife from the book. Deanna probably left Fredo off screen.

We do see her one more time In Godfather II after the communion party and the threat on Michael's life. She is sleeping with Fredo when he receives the call from Johnny Olla. After that it is anyone's guess what happened to her.

Man, she was hot. In the book she's a movie star and so probably became a trophy wife to Fredo without fully taking into account how much trouble she could be. I find it more strange that she'd go for him. Maybe she loved the thrill of being close to Mafiosi.

Well we know she didn't marry him for his dancing skills or his taste in clothing. I can still see that sport coat he wore to the communion.

Well Fredo was killed so I guess that made this easier for Deanna because she could go with who she likes

Deanna's marriage to Fredo was such a mystery. We know that they were obviously married at the time of the communion (she wanted to get closer to Michael-that tramp!). The last visuals of Deanna and Fredo is when Johnny Ola called Fredo to seek more info about the Frankie/Michael deal.
The last mention of Deanna is Fredo's confession to Michael that he wished he married someone like Kay at the cafe in Havana.

Deanna did not attend Mama's furneral. My personal belief is that after she learned about Fredo's estrangement with Michael: she took a hike!