Kat Von D claims Jesse James cheated on her with 19 women.
The tattoo model ended her engagement to the Monster Garage host in September.
James split from wife Sandra Bullock in April 2010, amid reports that he had been unfaithful to her with affairs with many women.
Kat has admitted that she now realizes that people who warned her off Jesse were right.
She wrote on her Facebook page: "Today I encountered the 19th girl to add to the list of people Jesse cheated on me with during this last year.
"I know I deserve a big fat ’I told you so,’ from everyone, and wish I didn’t have to say, ’You all were more right than you’ll ever know,’ but you were."
Despite her comments, Kat insists she is moving on from the "toxic relationships" and only feels pity for her former fiance for "seeking validation" with other women.
She added: "I kept going back and forth in my mind as to what the best way would be for me to release and let go of any residual feelings remaining from that toxic relationship.
"I think it just made me sad today to imagine him still in that dark place—where seeking validation through the attention of women takes precedence over being a good father, a sincere friend, a better co-worker, and a happy individual.
"I tried my best to go through all of this without venting, or complaining, or fueling more tabloid mumbo jumbo.
"But this is about me making peace with myself, and forgiving myself for making some bad mistakes."