The actor, who plays Bilbo Baggins in the new Lord of the Rings prequel, has been with Abbington for more than 11 years and they have two kids together, but she insists a trip down the aisle isn't in their near future.
Abbington tells Britain's Daily Mail, "So many people I know got married after being together for years and then got divorced six months later, and I think maybe we don't want to spoil it."
The 38-year-old, who met Freeman on the set of 2001 movie Men Only, is confident he would never cheat on her, although she admits she felt slightly insecure when he was cast in 2007's The Good Night with Hollywood beauties Penelope Cruz and Gwyneth Paltrow.
She recalls, "I did feel a bit funny then, because I was eight-and-a-half months pregnant and bigger than a house. Then I met Penelope and she rubbed my bump and said, 'Martin talks a lot about you.' She's beautiful and talented, so who wouldn't fancy her? Martin and I talk and joke about stuff like that.
"I trust him completely. We've got something so lovely and so special that you don't have to think about it. We are so sure that we love each other. Besides, he's a Catholic - any guilt would come flying out of him (if he cheated)!"