The troubled singer, 24, and Fielder-Civil, 25, have spent over half of their 11-month marriage apart after he was remanded in custody in November on charges of conspiracy to pervert the course of justice.
Before handing herself in to police for questioning over an alleged pub assault on Friday, the Rehab star spent the previous evening with rumoured new love Alex Haynes, 24.
Who's that boy?: Amy cosies up to Alex Haynes the night before her arrest over an alleged assault
Winehouse has been growing close to her manager Raye Cosbert's assistant Haynes over the last month, much to the delight of the singer's friends and family, who have made no secret of their dislike for Fielder-Civil.
Haynes has been described as a "clean-cut mummy's boy from Gloucestershire" - the opposite to self-confessed drug addict Fielder-Civil.
A friend told The Sun: "It is a relief that it's finally out and they have everyone's 100 per cent backing Alex is a good boy.
"He doesn't smoke or take drugs. He isn't a big drinker. Amy has really fallen for him."
Making her smile: Amy Winehouse clings to Alex Haynes during a night out in Camden
Despite still wearing her wedding ring, Winehouse was happy to be photographed holding hands and gazing into Haynes's eyes on a night out in Camden, north London on Thursday night.
The following day, Haynes was spotted in the back of people carrier with Winehouse when she arrived at Holborn police station for questioning on Friday afternoon.
Winehouse reportedly told music video assistant Fielder-Civil their marriage was over during a visit to Pentonville Prison on Monday.
Yesterday, the singer missed Fielder-Civil's court hearing at Snaresbrook Crown Court, where his trial date was set for June.
Support: Alex Haynes was also with Amy Winehouse as Holborn police station yesterday
However, blonde German model Sophie Schandorff, 21, was in Winehouse's usual place to support Fielder-Civil and the couple caused a stir by mouthing "I love you" to each other.
When asked about the nature of her relationship with Fielder-Civil, Schandorff said: "We are best of friends."
Fielder-Civil has pleaded not guilty to charge of conspiracy to pervert the course of justice in relation to an assault case.
He denies causing grievous bodily harm with intent to landlord James King outside the Macbeth pub in north London in June 2007.
Happier times: Amy Winehouse and Blake Fielder-Civil on their wedding day in Florida last May
A friend of the singer adds: "She has been fed up for ages and saying she wants to call it a day.
"All Blake does is scream and shout at her on the phone from prison and curse at her and his family blame her and criticise her.
"The trial is coming up and as it gets nearer and nearer the thought that he could come out has been on her mind — and it's not what she wants any more.
"Even the thought of having to go to court and publicly support him and see his family has been too much for her and has been doing her head in.
Courting attention: Sophie Schandorff and Blake Fielder-Civil mouthed 'I love you' to each other at his hearing yesterday
She has been turning up late and missing visits so she decided to just be straight with him.
"He burst into tears and was begging her.
"While he has been inside she has not been faithful to him and got herself in a position where he couldn't come back anyway because too much has gone on while he has been inside.
"She is filing for separation and making it official and has been celebrating ever since."
Winehouse was cautioned for common assault today after spending the night in Holborn police station in central London.
She has been accused of hitting a passer-by who hailed her a taxi outside a bar in Camden Town, north London, in the early hours of Wednesday after a six-hour pub crawl.
The self-confessed junkie is also alleged to have punched Moroccan musician Mustapha el Mounmi in the face because he did not give up a pool table in Bar Tok in Camden.
