Some fanfictions worth checking out are 'Soulbound'. This one portrays their connection as something that goes beyond the physical. 'The Scarlet Kiss' is a more romantic take on their relationship, filled with sweet moments. And 'Shadowed Love' shows how they deal with external threats to their relationship while also exploring their own feelings in depth.
One great Gambit x Rogue fanfiction is 'A Dance of Hearts'. It beautifully captures their complex relationship with lots of emotional moments. Another is 'The Red and the Black', which delves deep into their powers and how they interact in different scenarios. There's also 'Touch of the Thief', which has some really interesting takes on their shared adventures.
Well, 'Gambit's Gambit' is a popular one. In this fanfic, Gambit devises a plan to win Rogue's heart in a really unique way. Then there's 'Rogue's Redemption'. It shows how Rogue overcomes her internal struggles while her relationship with Gambit develops. 'Midnight Meetings' is also good. It focuses on their secret rendezvous and the tension between them.