Demi, who also appeared on Bachelor in Paradise, and Slater gave a big clue they're both single again when they unfollowed each other on Instagram. Demi, 25, also deleted photos of her boyfriend from her social media account.
In addition, Slater reportedly posted a selfie on his Instagram Stories on Friday in which he wrote, "So many ups n downs," along with a broken-heart emoji.
During a May episode of Demi's Big Demi Energy podcast, she admitted quarantining with Slater and his family amid the ongoing coronavirus pandemic created tension between the pair and they "fought a lot."
"[When] you spend that much time with someone and their family -- it's like you start nit-picking and you start getting mad over the stupidest stuff and fighting about it," Demi said, according to Us.
Demi also noted arguing in front of Slater's family took a toll on their relationship.
"I definitely feel uncomfortable at times, but I'm just trying to get over it but it's frustrating cause it's like, 'Babe' -- I'm like, 'Don't involve your family in all this because you know I'm here with you and it's going to be awkward for me and uncomfortable and I don't want that,'" Demi reportedly explained at the time.
Demi and Slater reportedly met through fellow Bachelor in Paradise alum Katie Morton, who had been friends with Slater for over two years.
Demi first teased there was a new man in her life in January when she tweeted, "Me telling my parents I'm talking to a guy with a lot of tattoos: so what y'all think? My parents: he's so camouflaged we can barely see him."
The following month, a source told Us that Demi was "happy" with Slater, which was around the time Demi first posted pictures with her new man on Instagram. One of the photos showed Demi and Slater kissing poolside.
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And in March, Demi gushed to the magazine about how she and Slater enjoyed "fun" date nights out such as bowling or mini golf.
Demi got involved with Slater less than four months after she and Kristian Haggerty, Bachelor in Paradise's first same-sex couple, announced on October 31 they had decided to end their engagement and part ways.
"What has always been at the forefront of our relationship is love and care for one another. Our priority is doing what is best for us. With a heavy heart full of love for one another we have decided it is best for us to take a step back from our relationship," Demi wrote at the time on Instagram.
"We ultimately want what is best for us in the long run and for us right now, that means being apart and growing individually... We will forever be proud of the impact our love story has made and we hope it has helped others feel more accepted and confident within themselves."
Meanwhile, Kristian has been dating YouTube star Taylor Blake, whom Kristian has known since they were both young teenagers.
Kristian initially shared photos with Taylor around Valentine's Day in which the women were being very affectionate with each other.
Demi and Kristian got engaged on Season 6 of Bachelor in Paradise last summer.
Fans began speculating their relationship was on the rocks in early October 2019, given they remained quiet on social media after posting photos of each other on September 19.
Demi assured Us on October 9, however, she and Kristian were just really busy and forced to spend time apart due to their hectic schedules.
"Every relationship is different and it's like -- I mean in the most respectful way -- it's nobody's business how our relationship works. We both have so much going on right now," Demi said at the time.
"Just because we don't broadcast [our romance] doesn't mean that we're not together... I think it's important to kind of have our space."
Demi and Kristian were both living in the Los Angeles area at the time but never apparently moved in together.