Jessica Simpson and John Mayer can't seem to get enough of each other: Just back from a romantic trip to Rome, they're making the amore last back in L.A. with kisses over lunch, nuzzles at a James Morrison concert and hand-in-hand strolls. And the 8-month-old relationship has passed the little-sister test. "Ashlee loves John," says a friend of Jessica's. "She thinks he is great for her. More importantly, Jess is happy."

So, it appears, is Mayer. "John seems very smitten," says another Simpson pal. On March 20 Simpson, 26, and Mayer, 29, happily snapped pictures with fans at a gig of Mayer's bandmate David Ryan Harris at the Hotel Cafe; the next night they hit Morrison's show at the Roxy. "They were smooching throughout," says a fellow concertgoer. Afterward they enjoyed cocktails at Parc restaurant with Ashlee. "They were holding hands and laughing constantly," says an onlooker. "Jessica looks really comfortable with him."

Friends say Simpson, who was divorced from husband Nick Lachey last June, is relishing this lower-key romance. "When she was with Nick, she was really under her family's thumb. This is a relationship that is all hers," says one friend. "Ashlee said Jessica is the happiest she's ever been in her life."

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