Ronnie Ortiz-Magro is finally opening up about the demise of his on-again, off-again relationship with Sammi "Sweetheart" Giancola, the only original Jersey Shore cast member who didn't return for Jersey Shore: Family Vacation.

Jersey Shore: Family Vacation premiered Thursday night on MTV, and Sammi's absence was a major point of discussion.

Ronnie also felt the need to address his tumultuous romance with Sammi that began on Jersey Shore in 2009 and lasted for eight years.

"Once we left the shore house, me and Sam decided we were going to take the next step -- we moved in with each other," Ronnie, 32, explained to his castmates, according to People.

"And we were getting towards that stage where it was like, 'I either have to sh-t or get off the pot.' She gave me a timeline. She was like, 'I want to get married in six months' -- and I'm still trying to figure my life out. I got cold feet."

Ronnie then revealed why exactly his relationship with Sammi ended for good and what was behind their nasty split.

"I wanted to do the right thing, but there was a part of me that was like, 'I'm not going to do the right thing.' So I didn't do it. I ended up cheating, she found out. I blew it. It's over," he reportedly confessed.

Sammi, 31, recently disclosed on Instagram that her reason for not joining her friends on Jersey Shore: Family Vacation was to avoid "potentially toxic situations." She said she's in "a completely different place" in her life right now, with a serious boyfriend and thriving businesses.

At the time the episode filmed, Ronnie's girlfriend, Jen Harley, was seven months pregnant. (The couple just welcomed a baby girl on Tuesday).

"It's not the most ideal situation, but what is?" Ronnie reportedly said in the premiere, telling Pauly "DJ Pauly D" DelVecchio the following: "I'll always be a sh-tty husband, I'll always be a sh-tty boyfriend, but I'll never be a sh-tty father."

Pauly D made light of the situation by introducing a life-size doll designed to resemble Sammi. Pauly D also cracked a few jokes at Sammi's expensive -- like having the doll whine, "Ronnnnn, stoppppp," with her thick, memorable accent.

Deena Cortese, however, wasn't happy with the direction things were going.

"Sam's my girl," Deena said. "We talk all the time, and I told her I wasn't going to let anybody talk badly about her."
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"Listen, I'll never say anything bad about her," Ronnie insisted. "She's a great woman, she's going to make a great mother, a great wife. She is absolutely amazing. She just was not for me."

Tension between Ronnie and Deena thickened later that night. Ronnie brought up Sammi again, saying she wasn't their real friend by opting out of this family reunion, which prompted Deena to suggest Ronnie wasn't over Sammi yet because he couldn't stop talking about her.

Ahead of Jersey Shore: Family Vacation's premiere, Ronnie spoke to People about the pros and cons of not having Sammi in the house with him on the show.

"On the one hand, it sucked because we all started this together so we wanted to end it together. But at the same time, it worked out better for me because it was just less drama for the house. Less fighting and bickering," Ronnie explained.

He reasoned, "Who really wants to live in a house with their ex? That's just the most uncomfortable feeling in the world."

"She's chosen a path in her life and she closed the door on Jersey Shore," Ronnie continued. 

"That was one chapter in her life, and now she's opened up another one, and she has a boyfriend and she's really happy and that's a decision that she made. And us as a family and as castmates and friends that have known her for so long, we're just going to support whatever she does."