The retired NFL player and Sports Illustrated model have been an item for quite some time, first meeting at a charity event in 2013. The pair had crossed paths earlier in 2013 while Gronkowski was a tight end and Kostek was a cheerleader for the New England Patriots, but they were never introduced to each other until they both attended the same charity event for the Patriots in November 2013. Kostek recalled their first interaction while appearing on SiriusXM's "This is Happening" with Mark Zito and Ryan Sampson by saying, "He ripped off his 'Hi My name is Rob Gronkowski' sticker on his T-shirt. He had written on the back of it his phone number." One of Gronkowski's teammates had actually given his number number to her first where she said, "I was a rookie. I was like, 'Oh no, no, no, I can't take this. I can't take his number.' And then his teammate was like, 'Just take it,' and I was like, 'Okay,' and I put it in my pocket. And I never spoke about it again."

The couple eventually Facetimed each other which quickly struck up a romance, but they would keep their relationship quiet for two years before taking things public. They made their red carpet debut in July 2016 while attending Nickelodeon's Kids' Choice Sports Awards. Ever since, the couple has been quite public with their relationship, whether that be Gronkowski attending events and supporting Kostek's cover of Sports Illustrated or Kostek cheering on Gronkowski during his Super Bowl appearances. Recently, Kostek shared a sweet set of photos on the couple's anniversary from the charity event that they first met at nine years prior with the caption, "9 years ago today we were volunteering at the @patriots Thanksgiving in a Basket event with @goodwillboston where Rob slipped me his number. Yes I broke the @patriotscheerleaders rules at the time and called him up … but it was worth it ❤️❤️❤️❤️."

Gronkowski recently hinted at the idea of the pair getting engaged anytime soon by saying that they were "both super busy with our careers right now" but "it's going to have to happen eventually."