** 1/2 Amy Rigby, “The Sugar Tree,” Koch.

As we have learned from this singer-songwriter’s two previous solo albums, love usually comes to her in seriously flawed forms, even as she hopes for something better.

Rigby keeps her sense of humor about that on “The Sugar Tree,” but patience appears to be wearing thin for this New-York-to-Nashville transplant, whose knack for chronicling the emotional travails of boho maturity has made her a critical favorite. Her hiccupy warble feels subdued, as if all the latitude she’s given to jerks of the moment has finally exhausted her.

If her put-upon-smart-woman-in-a-world-of-losers stance is feeling as tired as the contemptible desperation of the “Cathy” comic strip, Rigby’s wavering among mistrust, hopefulness, weakness and resolve remains endearingly human. Laced with gem-like bits of slide guitar and pedal steel, her songs still expertly incorporate ‘60s pop, gritty rock and country-folk twang. But although such melancholy drifters as “Sleeping With the Moon” are appealing, this collection is less biting and less exuberant.

Rigby finds respite in fantasy men, including a just-passing-through angel and a fondly remembered ex-lover who actually treated her badly. But these don’t alleviate the romantic enervation, which culminates in the languid country-jazz of “Cynically Yours.” It’s amusing that a heartbreak veteran accepts a lover simply because he’s not so rotten, but her lowered expectations are still a drag.

Albums are rated on a scale of one star (poor), two stars (fair), three stars (good) and four stars (excellent).