The 24-year-old's had an on-off romance with Aaron on Geordie Shore but, when they tried to give an off-camera relationship a go earlier this year, it didn't work.
Marnie then appeared on Celebrity Big Brother where she fell in love with housemate, ex-TOWIE star Lewis Bloor.
Speaking to OK magazine, Marnie said: "I just think me and him were fighting a losing battle. The last series, me and him just split up so many times – we were arguing, we just didn't work.
"I would never compare [Aaron and Lewis]. I would never slag off Aaron, but in a romantic way I am much more suited to Lewis."
She added: "All the [girls from Geordie Shore] have congratulated me [on CBB]. They're like my sisters. I haven't heard from the boys but I understand because of Aaron."
In a polite but firm tweet sent while CBB was on air, Aaron had said: "I honestly wish Marnie and Lewis all the best!! But any tweets regarding them from now on I will be blocking!! Bored of hearing about it."
Marnie and Aaron have had an on-off relationship for the last two years and Geordie Shore fans saw them finally seal the deal in an episode of Big Birthday Battle in May.
Meanwhile, Marnie revealed this week she's reached a major milestone with Lewis: meeting the family!
Marnie wrote in her Star magazine column: "Things with Lewis have been amazing. I met his family at the weekend! I was nervous but they felt they already knew me because they'd watched me on TV."
"For people saying we're a showmance, that's ridiculous," she said. "Since we came out we've kept everything private. I'm not putting any pressure on us – I've made that mistake before. We're really happy and I feel safe and confident.
"I've never met anyone like Lewis before."