Arquette first confirmed their romance last September, when he said in an interview he was so happy to be dating the "adorable" McLarty.
The former Dancing with the Stars competitor even told Howard Stern last November that he had fallen in love with his new partner.
Arquette took to Twitter on Wednesday (March 7) to confirm that he and McLarty recently decided to separate.
"Sadly I'm single again. A long distance relationship proved to be too difficult," the actor wrote.
Arquette was famously married to Friends star Courteney Cox. The two stars split in October 2010 after 11 years of marriage.
Cox recently said that she still gets on well with Arquette, even calling her estranged husband her "favourite person in the world".
> Courteney Cox: 'David Arquette was great on Dancing with the Stars'