The British singer's relationship with the Problem hitmaker broke down in late 2013, and he has now revealed the long-distance romance became "impossible".
The split came at a difficult time for Sykes, whose band The Wanted disbanded shortly afterwards, and he later poured out his pain in recording sessions.
He tells Britain's The Sun newspaper, "The time we broke up was really tough. The Wanted decided to break up and I lost my granddad. I was not in the best place. She was my first grown-up relationship. But sometimes you have to go into a place like that to be able to find the best music out of it.
"The most emotional song is about me telling myself not to be angry at the break-up because sometimes things just don't work out. That's life. No (Grande doesn't know songs are about her). But it's important not to be selfish with writing so there's no detailed version of events. And there's no bad blood. She's a lovely girl.
"We split because of the long distance thing. There was that amazing moment at the start of the relationship where we both convinced ourselves, 'Yeah, long distance won't matter. It will be fine'. But it was impossible."