12/13/2011 at 12:00 PM EST
With Hollywood breakups
running rampant, what's the secret to Jennifer Garner
and Ben Affleck
's successful seven-year relationship
"We both know we couldn't do what we do without each other," the actress says in the January issue of InStyle
, on sale Friday. "Ben always says, 'If you love it, we can make it happen.' "
Of course, jewelry helps, too! Affleck, 39, enjoys showering his wife with diamonds. He gave her a pair of pink and white diamond Harry Winston bands, one for each of their two daughters, Violet
, 6, and Seraphina
, who turns 3 next month.
"He knows when to swoop in with the gesture. He's sweet that way," Garner says. "Honestly, I would do anything for that man, because I know it's not taken for granted."
Also not taken for granted is their growing family. The actress, who is expecting her third child
, calls pregnancy at age 39 "a game changer."
Garner admitted to having a difficult first trimester, complete with nausea, exhaustion and junk-food cravings.
"My kids had never seen Doritos before. They would say, 'Mom, where did you get that orange chip? I really want that,' " she says. "I wish I was one of those cute pregnant girls who wear skinny jeans throughout their pregnancies. But I just gain weight."
See how Jennifer's look has changed over the years