Canadian pop star Justin and US model Hailey, daughter of actor Stephen Baldwin, have also told of the struggles in their marriage, and that it is not all a "magical fantasy".
The couple tied the knot in September after a 12-week romance, following a 10-year friendship.
In a joint interview, Justin, 24, told US Vogue magazine that he had a "legitimate problem with sex" before rekindling his relationship with Hailey - who he had dated briefly three years earlier - last June.
The Baby singer had chosen to give up sex for more than a year in order to feel closer to God he said, adding: "He doesn't ask us not to have sex for him because he wants rules and stuff. He's like, I'm trying to protect you from hurt and pain.
"I think sex can cause a lot of pain. Sometimes people have sex because they don't feel good enough. Because they lack self-worth."
Justin said he wanted to "re-dedicate" himself to God in that way "because I really felt it was better for the condition of my soul".
"And I believe that God blessed me with Hailey as a result. There are perks. You get rewarded for good behaviour," he added.
He told the magazine, on which they appear as cover stars together, their speedy marriage was partly down to their desire to be intimate.
He added: "When I saw her last June, I just forgot how much I loved her and how much I missed her and how much of a positive impact she made on my life.
"I was like, holy cow, this is what I've been looking for."
Justin said he believes she is trying to be a "grown-up" too soon, and that he thinks they can "be married and still have fun and enjoy our adolescence".
Hailey, 22, said: "It's just that I'm fighting to do this the right way, to build a healthy relationship.
"I want people to know that. We're coming from a really genuine place. But we're two young people who are learning as we go.
"I'm not going to sit here and lie and say it's all a magical fantasy. It's always going to be hard. It's a choice. You don't feel it every single day. You don't wake up every day saying, 'I'm absolutely so in love and you are perfect'.
"That's not what being married is. But there's something beautiful about it anyway - about wanting to fight for something, commit to building with someone."
She added: "We're really young, and that's a scary aspect."
Speaking of his personal struggles and "dark" times, including his battle with drugs and being "super-promiscuous", Justin also told the magazine that he is taking a step back from music for a while to "evaluate" himself.
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