'The Voice's Ryan Whyte Maloney Was Distraught Over Custody Battle, Fiancée Says

"The Voice" alum Ryan Whyte Maloney was locked in a custody battle with his ex-wife in the months leading up to his suicide ... and the dispute was taking a toll on his mental health, at least according to his fiancée.

Ryan's fiancée, Zana, tells TMZ ... Ryan and his ex-wife were fighting over custody of their four children for the past eight months. Zana says Ryan wanted to split custody with his ex, but she wanted primary custody -- and the back-and-forth was torturing him inside.

Zana says Ryan had a history of mental health struggles and was working on his issues before fatally shooting himself in Las Vegas.

TMZ broke the story ... the police report from Ryan's suicide says he shot himself after a heated argument with his fiancée while they were driving home. Cops said the couple was arguing about her jacket when he grabbed a gun from the glove box, hopped out of the car and pulled the trigger.

Ryan's fiancée disputes the assertion in the police report that he called her a "bitch" in an argument beforehand ... she's adamant he never spoke to her that way, and says she told cops SHE felt like a bitch that she was there when he died, and couldn't stop him.

Zana tells us she feels likes cops badgered her into making a statement. She says she didn't want to talk to police and wanted time to collect herself and give her statement later ... but she says cops said they wanted her to talk ASAP, and she gave in.

Zana says police misunderstood what she told them and took her words out of context. She says she asked Ryan if he had grabbed her jacket from the valet area of the New York-New York Hotel and Casino before they left ... but there was no argument.

Shortly after Ryan performed, Zana says, something was clearly disturbing him ... but she says he wouldn't tell her what exactly was the matter.

Ryan's fiancée says a celebration of life is planned for Wednesday night at Ole Red in Las Vegas, where his band will perform his songs with guest singers.

She says he wanted to be cremated so his ashes could be spread in a lake near his Traverse City, Michigan hometown.

Zana says she's remembering Ryan for the positive influence he had on his fans ... and she says whenever he walked into a room, everyone was excited by his presence and was eager to watch him perform.