"I haven't met two people that were more of soul mates than those guys," Graham recently told PEOPLE during her shoot for Foster Grant. "They are so absolutely amazing. Everyone loves them, and I really can't imagine him with anyone else."
And the couple – who got engaged in January, about six months after their romance first made headlines – haven't been shy about showing their love for each other. Most recently, the two packed on the PDA during Coachella.
"They literally are perfect – from their Humane Society work together to them wanting to make the world a better place," Graham shares. "I mean, it's really exciting when you see two people come together that are amazing."
In fact, Reed, 26, told reporters in February that the pair's morning conversations are about how they can make the world a better place, and the only thing she and Somerhalder, 36, argue about is the color of his eyes. "He thinks his eyes are ocean blue and I think they're aqua," the Twilight alum joked.
"[Nikki's] a pretty absolutely stellar person and she's actually now one of my best friends," Graham said. "I love that girl."