The couple exchanged promise rings with each other last month, reported Us magazine.
"I hear they were telling people they were promise rings, but I haven't seen Pattinson wearing one. They only told a few people about the engagement.
"They've been inseparable. He's planning on going to Coachella to support her. They've been living together and he's been calling her his greatest love," a source said.
It was reported in September 2014 that the Brimstone actor, 28, and the buzzed-about British singer (real name: Tahliah Debrett Barnett), 27, were dating.