The "Domino" singer, 35, posted her tribute on her Instagram Stories on June 3, a month after welcoming their baby boy and more than a year after suffering a miscarriage.
"Like a beam of light, he lit up my dark days," she wrote. "It was a whirlwind love and a miracle that we fell pregnant naturally with not one issue. Grateful doesn't cut it. He has given me many of the best gifts of my life."
Jessie continued, "He didn't let go of my hand and I wouldn't have been able to go through it without him. The calm to my crazy. The peace to my fear. The Daddy to my baby. Thank you."
The singer-songwriter officially announced the arrival of their son on May 19, and she couldn't help but express her overflowing love and joy.
"A week ago my whole life changed," she shared on her Instagram Stories at the time. "My son entered this world and my heart grew twice the size. The feeling is indescribable. I am flying in love."
"He is magic," she added. "He is all my dreams come true. He is my whole [world]."
Jessie has been over the moon about her pregnancy, which she first revealed on Jan. 6. In one of her Instagram posts in March, celebrating Mother's Day in the U.K, Jessie hinted at her blooming romance with her boyfriend, writing, "I love your Daddy so much, you wouldn't be on your way without him."
"He is the most patient, calm and good looking man," she continued. "You are going to LOVE him when you meet him."