Dolly Parton knows absence makes the heart grow fonder. The country music icon, 78, has been wed to her husband, Carl Dean, for 57 years — however, their lack of time together seems to be the key to keeping their romance fresh. “I’m just saying, anything new gets old,” Parton admitted. “I think if you just kind of stay together so much, you just nitpick every little thing and notice all that.” The “Jolene” vocalist, who doesn’t have any children with her spouse, 81, explained how their focus on their separate careers has made their times together more interesting. “It’s worked for us because w…