The Twilight star, 28, and his musician girlfriend, 27, are both sporting promise rings, a friend of the couple tells PEOPLE.
"He wants to marry her," the source says, describing his pal as "much more calm and happy than before."
"They are inseparable when they are together. They live at his house," the source adds.
Pattinson and the singer/songwriter – whose stage name stands for "Formerly Known As" twigs, a childhood nickname – were first linked after they stepped out together in Hollywood in September. He joined his new leading lady on her European tour in October, and the couple packed on the PDA during Art Basel in Miami at the end of last year.
They were last spotted out and about after the Brit Awards on Feb. 25.
Pattinson may remain hush-hush when it comes to his personal life, but he is "smitten," a Pattinson pal told PEOPLE in September when dating reports first surfaced.
The actor was previously linked to his Twilight costar Kristen Stewart. They split in 2013 after dating for three years.
Reporting by LIZ McNEIL
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