The pair split 18 months ago and the Brokeback Mountain actress was left devastated when he left her.
It's claimed Williams is taking things slowly the second time around for the sake of her daughter Matilda, five.
A source said to UK newspaper Daily Mail: 'Spike realises he made a huge mistake leaving Michelle and he desperately wants her back. They are making a tentative go of their relationship again but Michelle is nervous.
'Spike broke her heart the first time around. He's promised that he's a changed man who is ready for commitment, but Michelle has told him to prove himself before she trusts him again.'