The 19-year-old Australian actress, who recently quit her role as Nicole Franklin in Home and Away, said that she has a great relationship with sports star Myles because they have the same "aspirations".
James told New Idea magazine: "I think anyone who is married will tell you that when you know, you know. My mum always said to me that you should always be with someone who loves you more than they love themselves. And I think that's true with Nate.
"We're both easygoing and, while we're both in completely different professions, at the same time, they are very similar. We both have really high aspirations and want to do things together, like travel."
Myles added: "I thought it was the perfect time [to propose]. There are a lot of things I really appreciate about Tessa, but the thing for me is how easygoing she is.
"When I first met her, I thought by looking at her that she might be a little bit posh but she wasn't at all. She was funny - she makes me laugh. I've never gotten along with anyone like this."