Brown, 23, is said to have made special plans to spend his last days with the 25-year-old, reported Hollywood Life.
"He's just trying to basically spend as much time with his girl as he can before she leaves. He's just on top of his game with her now, hanging tough, being around her, buying her flowers and taking her to dinner because in a minute it's about to be a wrap," a source said.
Rihanna will begin her tour on March 8.