The "Toxic" singer is planning to go public with her latest romance this summer when she takes Day, who is still in rehab, to her cousin Erin's wedding.
The couple met at Malibu, California's Promises rehab facility during Spears' recent month-long stay.
The pop star has told close pals that she's smitten with her new beau, who hit the headlines following recent arrests on charges of disorderly conduct and allegedly verbally abusing a flight crew, while under the influence.
The couple was photographed playing tennis together at Promises on March 15, and Spears has been texting love notes to Day since she left the facility at the end of last month.
The pals reveals, "They formed a special bond. They were in group therapy together and Brit found his experiences fascinating.
"They would talk in their free time and try to have lunch together twice a week."
The couple plans to reunite when Day is released from Promises later this month.
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