The pair are said to have parted ways after almost a year together. It follows claims that Marcel got with another woman while they were on holiday together.
The Sun reports that Gabby has dumped Marcel over the allegations.
A source claimed: “She is mortified that he would do this when she was in the same hotel as him, so she's terrified to think about what he's done when she's not been around.”
Speaking out on Instagram and Twitter on Tuesday, Gabby told her followers: "Thank you to everyone for your kind messages, love and support.
"It's been a tough couple of days, I think I might still be in a bit of shock!
"But I'm sure in time I will be OK. I have the best family and friends around me. I'm a lucky girl."
The split comes just weeks after the couple denied they were 'on the rocks' following rows.
Speaking earlier this year, Marcel revealed that marriage and even kids were 'on the cards' for the couple.
"It's only been a short time, but marriage is definitely on the cards, 100 per cent," he said. "And once you're married, you start talking about having kids.
"We're going to take our time, but there might possibly be something coming up in the near future," Marcel teased.
He told new! magazine of a potential proposal: "I'll know when it is, and I'll obviously be preparing for that prior to the question being popped.
"Give it a year or so. End of 2018? Maybe the start of 2019? Who knows?!"
Meanwhile, Marcel reacted to Olivia Attwood and Chris Hughes' own Love Island spin-off show.
He said: "Them two together is drama, so it's going to be entertaining.
"Me and Gabs wouldn't get our own show because there wouldn't be any drama. It would just be us sitting there being happy."
If Marcel does pop the question to Gabby any time soon, they won't be the first of last year's Love Island couples to get engaged.
Dominic Lever proposed to Jessica Shears last September just weeks after the show.
"It happened the night before the TV Choice Awards," Jess said at the time. "We were staying in a lovely apartment in London. Dom filled it with flowers and had got us a bottle of champagne.
"I was grinning like a Cheshire Cat when Dom got down on one knee - he said afterwards that he had never seen me smile like that!"
Love Island will return to ITV2 this summer for its fourth season.