Scott Disick vowed that his family’s four-day trip to Costa Rica would be unforgettable. With E! cameras rolling, he and on-and-off girlfriend Kourtney Kardashian explored the jungle with kids Mason, 7, Penelope, 4, and Reign, 2; took a helicopter ride; and relaxed at their 30,000-squarefoot, $16,500-a-night rental, Villa Manzu. When the mood struck, “Scott proposed to Kourtney,” reveals a Kardashian source. “Not with a ring. He just said, ‘Let’s get married.’ ”
Kourtney wouldn’t engage. Set on keeping their relationship platonic after nine years of ups and downs, “she told him no,” says the insider. “Scott was embarrassed, upset and angry.” Fueling his distress: Disick, 33, had been on a two-year mission to win her back, getting sober at a Malibu rehab in 2015 and visiting clubs only for paid…