'Married at First Sight' Star Jessica Castro Suggests Ryan De Nino Was Unfaithful on Reunion Episode

— -- Jessica Castro and Ryan De Nino, who said "I do" on "Married at First Sight," are currently going through a very ugly, very public split.

On a reunion episode of the show, reportedly taped last month but aired on Tuesday, their bad feelings toward each other were on full display, as she raised suspicions he had cheated on her this past Valentine's Day.

"A week prior to that we had a blow-up because he told me that he was gonna be busy. So I didn’t see him. Not a card, not a nothing," she said. "A few weeks later, I find a Valentine's Day card from another female at his apartment."

"Because Ryan was trying to make it work with someone else, that’s why [our marriage] didn't work," she added later.

De Nino, however, denied being unfaithful and argued that he had tried to see his wife.

"I can't control people from sending me cards," he said.

Castro and De Nino were one of three couples who married for six weeks as part of the reality TV series on A&E’s FYI Network. While none of the marriages on the show appeared to have been successful, Castro and De Nino's break-up has been especially nasty. On Monday, a lawyer for Castro told ABC News that De Nino had threatened to kill her and her relatives, and that the objective now is to protect her from "all threats to her safety and well-being."

Though De Nino did not comment, he did post to Instagram a partial image of a restraining order filed by Castro, and wrote that he was "disgusted" by it.

On the reunion episode, however, Castro and De Nino explained what went wrong in their relationship. In addition to raising the infidelity suspicions, Castro, who admitted that she destroyed De Nino's watch after finding the Valentine's Day card, said that after the cameras stopped rolling, she and her husband made the choice to live apart. And while De Nino criticized his wife for not communicating well with him over the course of their marriage, he also apologized for the way he treated her.

"I am sorry. No matter what, it’s unacceptable [to speak to you the way I did] and as a man I need to take ownership of that," he said. "You think I don’t cringe when I watch this show? You think I don’t cringe when I see this stuff?"

After their conversation got heated -- De Nino walked out after Castro gave him $100 and said, "You need it more than I do" -- the two cooled off and were able to share a hug.

Meanwhile, the other two couples on the series also gave updates on their relationships. While Davina Kullar and Sean Varricchio agreed to get a divorce in the show's finale and have been estranged ever since, Ryan Ranellone and Jaclyn Methuen revealed for the first time that they weren't together anymore, either.

"After the process had ended, obviously it takes effort, and I'm guilty of not making a tremendous effort," Ranellone admitted.

However, after talking things over with Methuen and the panel of experts that matched them in the first place, they agreed to give their relationship a second chance.

Kinetic Content, the show’s producer, has told ABC News, "The experts on our show have the best of intentions and highest hopes for success for each couple. After undergoing extensive background and psychological checks by third parties, couples agree to be legally married on our show. ... Unfortunately, couples on the show can go through real divorces, and divorce can often be difficult."

"Married at First Sight" airs on A&E Networks, which is owned, in part, by Disney, the parent company of ABC News.