The actress, who plays Michelle Connor on the ITV1 show, announced her romance with Lomas at the Inside Soap Awards 2008 launch on Monday. She has been dating Jamie, better known as Hollyoaks' Warren Fox, for three months.
Jamie's ex-lover Hayley Lever, the mother of his two-year-old son Billy, has told friends that she is devastated by the news. Her pals claim that she is still hoping for a reconciliation with the actor.
A source close to Hayley told the Daily Star Sunday: "She is very upset about the whole thing. She thought she would spend her life with Jamie and she is shattered. It hurts because Jamie still visits to see Billy, so she sees him a lot. It really is agony for her. But she is prepared to fight to get her man back."
Marsh ended her six-year marriage to former EastEnders actor Jack Ryder in March.