The actor, who has played Alex Moss since last April, insisted that the pair's relationship is not "a cougar situation".
"I don't believe it's a cougar situation. I believe they actually like each other," Stacey told PA.
"Alex isn't looking at her age, he's not even thinking about that. He's just thinking, 'I like this woman. Oh, she likes me!'
"And then when they get it on, age wasn't even a factor. It was just something that was there. It was just pure attraction. It's not about age, it's not a fantasy for Alex."
The 21-year-old added: "It's really passionate. We've made it a lot more serious, as much as possible, so people will see these people like each other.
"It's not just a one-off. It's something that I'd like them to always look at and remember. It won't just blow over."
Seeing the plot in a different light, Stacey's co-star Natalie J Robb - who portrays Moira - recently said their attraction is based on "fun and sex".
The 37-year-old also revealed that Stacey "went for it" during their upcoming romantic scenes.
Moira and Alex's secret relationship will begin in an episode to air next Friday (August 10) on ITV1.