With Bruce Willis's 10-year marriage to Demi Moore now officially over, the Unbreakable actor is speaking out about what caused the seemingly rock-solid union to sour.

"Things change," Willis tells US Weekly. "People grow at different rates. People change at different rates. It's difficult for any couple to keep their marriage intact under the best of circumstances, and our marriage was under a huge magnifying glass all the time. So it might have been a little more difficult for us."

Willis — who declined to discuss his recent split with Spanish beauty Maria Bravo — admitted that he has yet to pinpoint the specific cause of his failed marriage. "I haven't figured it out yet," he explains. "I still love Demi. We're very close. We have three children whom we will continue to raise together, and we're probably as close now as we ever were. We realize that we have a lifelong commitment to our kids. Our friendship continues. The institution has been set aside.

"Any form of a relationship ending is a painful thing," he adds. "The only thing I really know is, time is the only thing that heals any pain."

The 45-year-old multi-millionaire says that he's currently single, and plans to stay that way for now. "I'm taking a year to myself," he reveals. "I've been in and out of a relationship for the last 18 years, and I decided that I'm going to take a year to myself. See what that's like. That will be a far more unique experience to me than jumping back into a relationship."