Credit: Stefanie Keenan/

One Tree Hill is nearing its long-awaited series finale -- and not a moment too soon for CW star Sophia Bush, 29.

The actress has split with her on-and-off beau of six years, Austin Nichols, 31 -- the third guy she's dated from the just-wrapped TV hit -- a source tells the new issue of Us Weekly (on stands Friday).

Bush broke it off with Nichols (who plays her husband) "because she didn't think he was the one," explains a source. "She's moving on."

The actress was wed to Chad Michael Murray in 2005 and dated James Lafferty in 2009. The final episode of One Tree Hill airs April 4 on The CW.

Tell Us: Are you surprised Sophia Bush and Austin Nicols are over?