The 36-year-old, who helped steer Team Oracle USA to a famous comeback victory in the America's Cup, has known Thompson for three years.
"We met through friends at an event, and I don't really know how to describe it," Thompson told the Daily Mail. "It was a bit of a thunderbolt moment but a thunderbolt that took years before it became anything real.
"We were in different places but then in April the stars aligned and it made sense to be together, and we haven't looked back since. It's very special, he makes me very happy."
Thompson, who now works for Fox Sports in the US, had a previous two-year relationship with ITV presenter Declan Donnelly.