Hanson popped the question a few weeks ago in a Hollywood hotel as family and friends watched. "He's the perfect partner for me, and I feel like we evolve," the actress says. "When you're so into somebody and you get to just mush up next to them - that's the best part of it."
Vangsness was previously engaged to Melanie Goldstein in 2009 after the couple dated until 2009.
"I was so in love with her, but in terms of life growth, what we were both doing separately was just pulling us apart, not sexually, but in all other ways in terms of what your dreams are and what you want to go after and all that," Vangsness says of her ex.
The actress is very excited about her future with Hanson, even if she wasn't expecting to be planning a happily ever after with a man. And yet, she still doesn't consider herself bisexual.
"I guess I never understood the term of being bisexual because once I let myself come out 10 or 12 years ago, I was like, 'Oh, okay I'm gay,' and I was perfectly okay with that, but then I was like, 'Wait, nothing changed in me,' " says Vangsness. "I don't feel any different."
When it comes to planning the special day, Vangsness says that her husband to be will be on deck to help with the ceremony.
"He's more particular than I am, which is going to be fine, but he has many more requirements than I do," Vangsness says. "It might take a little while longer, but it's a quality problem."
VIDEO: Criminal Minds' Kirsten Vangsness answers your burning questions