has been living on a bus for her sell-out "Blown Away" tour for the better part of eight months now.
But even while on the road she has constant motivation for staying in shape: her hard-bodied husband, NHL star Mike Fisher
"Even when he's like, 'I'm so out of shape,' he still has a six-pack," she tells PEOPLE in this week's cover story. "Having Mike there – I want to be a hot wife!"
Although she acknowledges that the frequent distance between them can be challenging, the six-time Grammy-winning singer
, 30, says she would walk away from her career if it ever started to cause problems between her and Fisher, 32.
"If Mike ever told me he needed me to quit, I'd quit," she says. "When you make that promise to somebody, and you stand before God and your family and friends, you've got to do everything that you possibly can to make that work."
For Underwood and Fisher, who will celebrate their third anniversary in July, making it work means frequent texts, hosting wine-and-grill nights at home with friends and meeting up for casual dates – at Subway.
Says Underwood: "We called it 'our place' when we were first dating!"
For much more from Carrie about her marriage and her plans for starting a family – and exclusive photos from her Oklahoma childhood and behind the scenes on her tour – pick up this week's PEOPLE, on newsstands everywhere Friday