Britney Spears and Jason Trawick
11/30/2011 at 08:00 AM EST
is getting ready for her 30th birthday on Friday and will finish up a successful world tour next week – but that's not all she's gearing up for.
A source close to the singer tells PEOPLE that an engagement is imminent for the pop star and longtime boyfriend Jason Trawick, 39, who sources say has picked out a ring.
"They’ve been talking about marriage for a long time," says the source. "It would be surprising if they are not engaged by the end of the year."
Adds the source: "Britney is really looking forward to turning 30. She is having one of the best times of her life."
Reporting by JENNIFER GARCIAFor more on Britney's milestone birthday, her relationship with Trawick and her sons, and what her life is like now, pick up the new issue of PEOPLE, on newsstands Friday