The couple - who got engaged in February 2015 - recently called time on
their five-year romance and insiders believe their conflicting schedules
caused the break-up.
A source told PEOPLE: "Their work kept them apart a lot. 'Chicago Fire'
keeps him in Chicago and her work is almost always elsewhere."
The pair haven't been pictured together recently and she hasn't shared a
picture of him on her social media accounts for over a month.
Last week, on Taylor's 35th birthday, Gaga, 30, was seen without her engagement ring while she was out and about in Malibu.
Taylor and Gaga met on the set of her 'You and I' video and she
previously revealed how they kept their long-distance romance alive.
She said: "We don't have any rules about calling each other at certain
times ... We'll go days at a time without talking and then we'll talk
every day. He's on his journey and I'm on mine and we're gypsies. And
then when we're together, we're really in love and that's it."
And she explained that her mother Cindy was in charge of planning the nuptials.
She said: "I think if I wouldn't let my mom do this with all of us and
my family - I think if I would've denied the women of my life the
planning of the wedding - they would probably kill me. I have all the
help in the world in a way!"
The 'Born This Way' hitmaker was adamant her wedding to actor Taylor was going to be low-key.
She added: "We are not planning anything that is worth writing about."