The 40-year-old Beady Eye frontman and his former aide are said to have been secretly involved even before his marriage to Nicole Appleton fell apart in July, reported Contactmusic.
"Liam saw her as the one person he could trust with anything. Some of us think she's gone mad and have pointed out Liam appears to have had four kids with four different women. But Debbie is besotted and is convinced they have a future together," a source said.
Gwyther, 31, was earlier spotted getting too close to the singer.