Jennifer Garner and Ben Affleck
04/19/2005 AT 09:00 PM EDT
Ben Affleck and Jennifer Garner are engaged to be married, PEOPLE has learned.
Though neither Affleck nor Garner will officially confirm it, a close friend of his has been spreading the word that the couple are going to tie the knot. This echoes a prediction that one of Garner's childhood friends made in early February when she noted that "it's my understanding he's going to give her a ring."
The Hollywood pair spent the weekend in the Los Angeles area celebrating Garner's 33rd birthday (April 17), including a party Saturday night at her Brentwood home with her parents, pals and some co-stars from Alias.
Affleck, 32, and Garner, who co-starred in 2003's Daredevil, have been dating since August 2004. But except for occasional appearances together at Boston Red Sox games and low-key events, the couple have kept their relationship mostly out of the paparazzi limelight.
Affleck, for example, didn't accompany Garner on the red carpet of the Screen Actors Guild Awards in January – or to the premiere of Elektra that same month – but joined her at the SAG after-party, where one observer told PEOPLE, "They both seemed really happy all night."
In February, Garner visited Affleck on the set of his upcoming film Man About Town in Beverly Hills, where between takes "they were smiling and holding each other," a witness told PEOPLE. "They didn't seem to care (that people were watching.) They looked really happy, looking into each other's eyes." Said a friend of the couple's: "(They're) like high school sweethearts. They're very lovey-dovey."
Both stars have experienced previous high-profile relationships – and break-ups. Affleck was engaged to Jennifer Lopez, but after postponing one wedding date in September of 2003, the couple eventually ended their romance.
In April 2003, Garner split from her husband, former Felicity actor Scott Foley, after 2 1/2 years of marriage.