Dolly's character knows his behavior and warns him that she can’t trust him because "once bitten," twice shy—a lesson she clearly learned the past that's now coming back to sting her in the present moment that the song captures.
He has returned, looking for another try, but Dolly's got the upper hand as the narrator: she knows this won't end well—he'll go to her as much as will he'll "chase a rainbow after rain"—leaving again as soon as the good times turn back over into hard times once more.
Dolly’s the wiser person now; the song plays through with a bittersweet tone on her side: the regret on both ends of the "Here You Go Again," but acceptance that you can’t teach your heart not to feel—the "I can’t help my soul" in Dolly Parton's song—no matter who is involved or how things ended (or will inevitably go again.)