'Jersey Shore' Personality Ronnie Ortiz-Magro Opens up About Cheating on Sammi Sweetheart

What's Jersey Shore without Sammi Sweetheart?

Half of the original MTV series' drama stemmed from the tumultuous on-again, off-again relationship between Ronnie Ortiz-Magro and Sammi "Sweetheart" Giancola, which lasted for almost eight years.

So when the Sammi opted not to appear in the Jersey Shore Family Vacation reboot of the show, which premiered Thursday, April 5, it was only a matter of time before her absence was brought up on the show.

(Sammi has since explained herself, saying, "I'm at a completely different place in my life right now focusing on my businesses and my relationship," in an Instagram posted earlier this week.)

In the two-hour premiere Thursday, Ronnie also opened up about what broke up the couple once and for all after they left the shore.

"Once we left the shore house, me and Sam decided we were going to take the next step — we moved in with each other," he explained. "And we were getting towards that stage where it was like, I either have to s— 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," he continued. "I got cold feet. 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."

Sammi's not the only one who has moved on. At the time of filming, Ronnie's girlfriend Jen Harley was seven months pregnant, and the couple welcomed a baby girl on Tuesday.

"It's not the most ideal situation, but what is?" Ronnie said to roommate Pauly "DJ Pauly D" DelVecchio. "I'll always be a s—y husband, I'll always be a s—y boyfriend, but I'll never be a s—y father."

The rest of the cast also missed Sammi as they moved into their reunion house in Miami, but Pauly D did his best to lighten the mood, bringing in a life-sized sex doll designed to look and talk just like their old roommate.

But as jokes were inevitably made at Sammi's expense, Deena Cortese intervened.

"Sam's my girl," she said. "We talk all the time, and I told her I wasn't going to let anybody talk badly about her."

"Listen, I'll never say anything bad about her," said Ronnie. "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."

As the episode wore on, tensions between Ronnie and Deena, 30, continued to simmer, especially once everyone had a few drinks. Finally, he confronted her at the club in classic Jersey Shore fashion.

"She's not here. She's not our friend. She doesn't have our backs," he said. "Because if she did, she'd be here with us. I'm having a motherf—ing kid and I'm still here. What the f— does she got going on that's more important than me?"

"Why are we still talking about Sam?" said Deena. "He has a pregnant girlfriend at home, and I still clearly he's still not over her. That's not good for him."

Later, Deena revealed the deeper reason she was feeling resentful towards Ron. After her dad died, he was the only cast member that didn't reach out to her. When she finally brought up how much that hurt her, he apologized and the two made up.

"When Deena's dad passed away, I was in a bad place," he said. "Me and Sam had broken up. I was going through my own personal stuff at the time — depression, or whatever you want to call it. I was dealing with my own issues, and I made a mistake by not reaching out."

Jersey Shore Family Vacation airs Thursdays at 8 p.m. ET on MTV.

Photo credit: MTV