Once Mari broke the news to Kenny that she'd like them both to remain open to dating new arrivals on the beach, Demi made a move on Kenny and bragged about how "all is fair in love and war."
Mari and Demi got into a heated spat over Kenny, and at one point, Mari even threw a birthday cake Demi had made for Kenny's 40th birthday into a bonfire.
Mari subsequently told Kenny that she wanted to continue their romance, but Kenny, afraid his relationship with Mari had become "toxic," decided to go to "The Boom Boom Room" with Demi and then continue pursuing their sexual and fun relationship.
After Demi gave Kenny a rose, she was displeased when Tia Booth arrived in Paradise and asked Kenny out on a date. Kenny not only said "yes," but the pair sparked a connection and played a naked game of volleyball with strangers.
"Life is hard when you're dating the hottest guy on the beach," Demi said. "It hurts the ego a little bit, I'm not going to lie... [But] he'll be back. I know I'm more fun. I am fun, playful and sexy, and I think Kenny really likes that."
Meanwhile, Mari still had feelings for Kenny and said she missed him and was prepared to fight for him, and so Kenny found himself in a love triangle -- and a bit of a pickle.
Mari shared with Kenny once he returned from his date with Tia how she still really liked him and didn't enjoy watching him with other people.
"I felt so strongly [for you] that I got scared," Mari confessed. "I knew what was there... and I never felt so strongly for someone so soon and... I've been thinking about you this whole time."
Kenny told the cameras it was tough and it "hurt" to be totally focused on Mari and then hear her say she wanted to explore Paradise with other men. However, Kenny said he liked Demi but definitely had "something special" with Mari.
Kenny struggled to regain trust in Mari, but he declined going to "The Boom Boom Room" with Demi again, which was a clear indication of which woman had captured his heart at that point.
"I wanted Kenny to fight for me. I wanted to feel solidified with him, but I just feel like he's waiting for Mari," Demi told the cameras.
"He's, like, obsessed with her in some weird, f-cked up way. I did not fight this hard just to be placed in his pocket. That's a sh-t feeling and I feel like an idiot!"
Mari later sat down with Kenny and said she really liked him and cared about him and wanted to be with him.
Mari promised Kenny that her intentions were pure and she wasn't just after his rose.
"I've been about you the whole entire time," Mari noted.
Kenny admitted his feelings for Mari were "pretty strong" from the start and he couldn't even explain why. He said there was "something different" about their connection and he never felt this way about a woman before.
Kenny then kissed Mari, and Demi was left feeling like a used one-night stand.
"Why do you want her?! A girl who is stuck-up as f-ck? She's so completely different from me," Demi yelled at Kenny.
"[Mari] thinks her sh-t doesn't stink. She's rude to everyone. So is that what you like or do you like someone like me, who's playful and funny?... She's evil! She's a mean, mean girl. She's a pageant girl!"
Despite Demi's negative view of Mari, Kenny and Mari proceeded to fall for each other more and more every day in Paradise.
Kenny and Mari then entered "The Boom Boom Room" together so they could take their relationship to the next level. Mari said they had put their relationship to the test and came back even stronger from it.
"Obviously I knew Kenny was hot," Mari gushed.
"I knew I was attracted to him and there's a lot of physical chemistry between the two of us, but just seeing how he's slowly but surely been more expressive about his feelings and opened up to me, he's shown me lots of different sides of him."
Kenny eventually gave Mari his rose and then the pair was able to go out on a date.
Kenny and Mari essentially created edible art by putting tacos all over each other's naked bodies before eating them off. It created a new level of intimacy for the couple, and Mari told the cameras she was "falling in love" with Kenny.
"Mari is the hottest plate I've ever seen. She is a freak. Behind closed doors, you've got to watch out," Kenny disclosed.
Kenny told Mari that it didn't scare him to talk about being together after the show and he'd be willing to talk about getting engaged soon.
"I believe in what we have, and I really do think we're going to be good after this," Mari told Kenny.
Kenny said he was "falling in love" with Mari, and she replied, "That's funny because I am falling in love with you too. [I am] 100 percent [sure]."
In addition, the preview flashed a brief clip of a man's hands opening a ring box to display a flashy diamond engagement ring.
That man was clearly Kenny!
The network accidentally spoiled the bachelor's identity because the gold chain Kenny always wears around his neck is on full display in the background and part of Kenny's blue chest tattoo is clearly visible as well.
Kenny has a large tattoo on one of his pecks that is a depiction of the American flag with red, white and blue colors -- stars and stripes.