Stars do not convert to Love. Sessions has different systems with different objectives, and Stars are used to place you in a weekly leaderboard competition between Artists. Love, on the other hand, is a digital currency that you can cash out for real money, mostly received from donations from your Fans.
See also: "Help Article: What are Stars?" vs. "Help Article: What is Love?"
While earning Stars might place you in a good position in the weekly leaderboard competition (and earn you Bonus Love) and make you reach a higher Artist Level (earning you unlockable rewards), they don't translate to Love directly.