The singer dated the BBC Radio 1 DJ from June 2010 before splitting in January.
She explained that she thought the romance would "last forever", and didn't realise how fame would make it difficult.
''I was naive to think my relationship with Greg James wouldn't be in the spotlight," she told the Daily Mail. "I fell in love with him because he's very positive and intelligent and a really good person.
"I thought it would be fine, that it would last forever. That I had fallen in love with someone so purely and simply was amazing to me. It was very sad that it didn't work out and was down to factors such as not being able to see each other much.
''When I was young I would read about people who had broken up because they hardly ever saw each other and I would think, 'That's rubbish. You can always make it work if you're in love'. It's so sad to me that you can't - so much about a relationship is about being together.''
Goulding has been dating dubstep producer Skrillex - real name Sonny Moore - since February, which she said was unexpected.
''I became very good friends with Sonny when we worked together and after that we realised we wanted to spend a lot of time together. Although we are very similar, I didn't see it coming at all, especially after such a sad time breaking up with Greg.
"Sonny is based in Los Angeles but sort of lives in hotels. I've been splitting my time between my work and seeing him on tour because he pretty much does a show every night, so if I want to see him, I go along.''
Ellie Goulding will release her second studio album Halcyon on October 8.
Listen to Goulding's new single 'Anything Could Happen' below: