Marco Donatelli has been one of the few "Love Island USA" winners to successfully stay together with his coupled-up partner ... and he tells us he's firmly in Pepe Garcia 's corner -- who recently revealed to us his own 'LI' relationship is donezo.

We caught up with the twin-like island lads in Beverly Hills ... they tell us they met through the island grapevine -- Marco is the show's Season 5 winner, and Pepe was a finalist on Season 7 -- and they've been leaning on each other for support after time in the villa. Getty

Marco and his fiancée Hannah Wright announced their engagement back in May, and he shares there aren't any locked-in wedding plans just yet ... but he's ready to get the ball rolling in the kid department.

MD also says his new bestie Pepe will without a doubt

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