Jennifer Garner, the 51-year-old star of "Yes Day," is reportedly hesitant to marry her longtime boyfriend, 45-year-old CaliBurger chain CEO John Miller, due to lingering fears from her failed marriage to Ben Affleck, according to sources, Globe reported.

Garner, who first met Miller in 2018, is said to be concerned that marriage could jeopardize their relationship. The couple briefly separated before reuniting, insiders claim.

"John treats her like a princess and she's madly in love with him, but taking that step forward is daunting and kind of scary for Jen," reveals a source.

The insider adds that the couple has been engaged for months, but Garner is hesitant to wear the ring or plan a wedding, as the prospect of entering into a formal commitment frightens her. "John's totally patient, he understands, but a lot of Jen's friends think it's sad and holding her back as far as that happily-ever-after she richly deserves."

Garner was previously married to actor Scott Foley and later to Ben Affleck, with whom she shares three children: Violet, 17, Seraphina, 14, and Samuel, 11. As previously reported by GLOBE, Affleck's addiction issues contributed to the couple's separation in 2015 after ten years of marriage. Their divorce was finalized in 2018.

"Truth is, Ben did a major number on her faith in marriage, and she'll probably never fully heal," shares the insider.

Garner is aware of Miller's wonderful qualities and how different he is from Affleck, but she remains apprehensive. The source explains, "It's not the wedding she fears, it's what comes afterward. It's so great now, so why rock the boat?"