Nick and Vanessa Lachey "make time to prioritise each other"

Nick - who has Camden, 11, Brooklyn, nine, and Phoenix, seven, with his wife - told PEOPLE: "Sometimes you have to be deliberate. You have to make deliberate attempts because the spontaneity, the romance, whatever you want to call it that existed pre-kids, it just can't exist the same way.

"And I would argue that it shouldn't exist the same way because your priority should be your kid, but you have to also make time to prioritise each other.

"And if you lose sight of that and lose track of that, then I think that's when you can get into some trouble."

Nick stressed that there should be "no shame" in approaching any romance in such a "deliberate" way.

The singer explained: "Make it deliberate. There's no shame in that. You've got to make it deliberate.

"Make time for each other, make it a scheduled thing if you have to, but make sure you give that to each other."

Nick also identified good communication as another key to their happiness.

The pop star - who was previously married to Jessica Simpson - said: "We've always said and been very vocal about the fact that you got to remember where it started and stay true to that. And you've got to make time for each other, whether it's a vacation together or even a weekend together or a night together.

"There's nothing more important in our lives, or in life, than your children. But you also have to always honour and respect and prioritise the relationship that got you those kids. So that's what we always try to maintain."