Russell and Danielle had an on-again-off-again relationship since 1989, with the pair marrying in 2003, before welcoming their two sons Tennyson, nine, and Charles, 12.
Danielle called it quits on her nine-year marriage with 52-year-old Russell in 2012.
Read more on Spy:
• The real reason Sam Hayes didn't quit TV3
• Inside the private life of Julian Savea
The Romper Stomper actor was reportedly trying to come to terms with Danielle's new boyfriend Adam Long spending time with his sons.
"The thought that someone else is spending more time with them than he is - and is slotting into life with his entire family - anyone would feel jealous," a source allegedly told Woman's Day.
"It's never easy to watch someone move on and be happy with someone else, but everyone knows Russell has and will always love Danielle."
The New Zealand-born star told The Sunday Times newspaper: "I've loved Danielle Spencer since 1989 - that's never going to change - and that's one of those things where I stare at her and go, "How did this fail?"
"I still can't work it out, because my feelings for her have never changed."
Asked if there was a chance of a reconciliation, he added: "Once I commit to something, I stick with it, so you never know..."
30 Odd Foot of Grunts formed in 1992, before breaking up in 2005.