"I was so nervous. I liked Tristan so much," Kardashian began. "It was after a night of us hanging out and we were with a bunch of friends at one of their houses. We were all drinking and telling stories and just enjoying each other's company."
"I forget what led up to that moment, but I do remember that we both started kissing in the kitchen -- in front of everyone. I think we were really passionate, so we made everybody a little uncomfortable, LOL!" she wrote. "It was pretty magical! I never want to forget that moment."
As for what the lovebirds have planned for Valentine's Day, she said they'll be spending the day with family.
"We're both not very needy when it comes to this kind of stuff, so we're just going to go to my mom's and have a couples' dinner with my family. Cute, right?" she said. "But I'll be doing some cooking too! Tristan is Jamaican and he absolutely loves Jamaican food. He could eat Jamaican food seven days a week 365 days a year. His mom has been teaching me how to make authentic recipes, so I will be making him an amazing Jamaican meal earlier in the day."
"If I'm craving something, I make sure I give it to myself," she insisted. "During my pregnancy, I'm obviously not beating myself up about what I'm eating at all! I'm more encouraged by how, after the baby comes, I'm going to work off every pound. I'm actually really excited to get my body back. I can't wait!"
See what she told ET about working out while pregnant -- and which sister is giving her the most advice -- in the video below.