The motorcycle entrepreneur - who was married to Oscar-winning actress Sandra Bullock for five years until 2010 - called off his engagement to the tattoo model last month but has now realised how "special" she is and their plans to marry are back on.
Jesse told People: "Sometimes you are only given one chance in life.
"It was up to me to open my eyes and see it. That girl is my chance. I will never stop fighting and striving to hold on to her. Showing her how special she is, and how much I love her."
The pair posted photographs of themselves embracing on their twitter pages, with Jesse adding the caption "para siempre", Spanish for `forever`.
Jesse admitted he "really loved" Kat when he called off their engagement, but said they split because of the distance between them, with him raising his children Chandler, 16, Jesse Jr., 17, and seven-year-old Sunny, in Austin, Texas, while the brunette beauty lives in Los Angeles.
He said: "I`m so sad because I really love her. The distance between us was just too much."
However, Kat`s TV show `LA Ink` has recently been cancelled, so it is unclear whether she plans to move closer to Jesse.