The I’m A Celebrity star popped the question during a romantic trip to the Lake District.
He told HELLO! he met Harry a few days after Christmas at a jewellers in Bournemouth to pick out a platinum and diamond cushion cut ring.
James, 25, said: “Harry said he knew a really good jeweller whenever I was ready to do it and I thought, I may as well just do it.
“By the time Harry arrived I had already chosen the ring; as soon as I saw it I knew it was the one. And Harry loved it too.”
“I missed her so much when I was in the camp and I really struggled.”
The Vamps star got down on one knee to ask his 23-year-old girlfriend to become his wife after celebrating the New Year together.
But he struggled to get the words out because he was overcome with emotion.
Once he’d stopped crying, Kirstie said: “Aren’t you going to ask me then?”
Guitarist James met model and environmental student Kirstie four years ago.
He grew close to football manager Harry during their stint in the jungle at the end of the last year.
He previously admitted his marriage to Sandra inspired him to pop the question to Kirstie.
the I’m A Celeb star said: “Harry and Sandra are the true love story. It’s very easy for us all to think it doesn’t exist. But it really does.
“They met when they were 17, courted for four years, then got married. They’re definitely the example that’s made me realise Kirstie and I are very happy with what we’ve got and we want to kind of do it really.
“He’s given me the inspiration to take the next step.”