It's not just a source saying it... it has now been confirmed!
Justin Timberlake, 30, and Jessica Biel, 29, have ended their relationship after four years of dating. Reps for the former couple issued this joint statement today: “Addressing the media speculation regarding Jessica Biel and Justin Timberlake’s relationship, we are confirming that they mutually have decided to part ways. The two remain friends and continue to hold the highest level of love and respect for each other.”
I would've thought that they'd have an open relationship.
Also, Justin Timberlake never seemed to have a libido. Like, I know he sang the song about sexy backs and all that, but he never seemed particularly horny at any point in his life. Then again, his last squeeze was Cameron, and she's it in the Madonna-Kate-Cameron rotation for A-Rod right now, so perhaps he got it on with her.