Writing in her new column for Star magazine, the Geordie Shore star said things have been tricky with Lewis lately but declined to go into specific details.
"It's been a difficult week with Lewis and I having a two-day argument, but my friends have been amazing. I love Lewis, but he needs to make some changes to the way he behaves if he wants our relationship to work," she wrote.
The two reality stars met on the summer series of Celebrity Big Brother and quickly fell for each other in the house, becoming utterly inseparable and smitten.
But, after the show ended, they admitted being in a long distance relationship has its strains: Marnie lives in Newcastle, where Geordie Shore is filmed, while former TOWIE star Lewis is based in Essex.
A rumour surfaced last week that they'd split after Marnie deleted all trace of Lewis from Instagram, but she later clarified on Loose Women they'd simply had a row.
"It's really tough because we live so far away from each other," she explained.
"We had an argument and I deleted every picture of him on Instagram. I was really angry and immature and forgot everyone can look at it. I thought, 'Why have I done that?! I've put so much pressure on us.'
"It's hard, but we're working through it.
"Things on the outside are very different to how they are [inside the CBB house] and we have kind of got a completely different relationship to what we had in there, so it's back to basics."
Marnie has not said what the argument was about.
They do seem to have got things back on track, however, as Marnie shocked fans on Friday by sharing a Snapchat of Lewis walking around completely naked!
While we watched them fall for each other in CBB, the couple made the decision when the show ended to remove their romance from the limelight, turning down the chance to do joint photoshoots or television appearances.