The pair first fell in love while shooting hit 2008 musical Mamma Mia! in Greece, but their romance hit the rocks due to their hectic work schedules.
Cooper was linked to another actress, Ruth Negga, who is now his girlfriend, in 2009 while they were still dating, and Seyfried admits it broke her heart to see the allegations in the press.
But despite their troubled past, the Les Miserables actress is adamant she will maintain a friendship with the Brit no matter who he is dating.
She tells Elle magazine, "I got my heart broken pretty hard. I was just kind of foolishly thinking that the two of them (Cooper and Negga) were done and Dom and I were involved.
"Dom and I love each other... he'll always be in my life, regardless of what his girlfriends or future wife think. I'm never going to be with a guy that can't deal with my friendship with him.
"Love and relationships are always going to be complicated and wonderful and difficult to hold on to. That's the incredible thing about love - it just overwhelms you at times and makes you do things that maybe you wouldn't or shouldn't do. Love can be scary that way but it can also take you to incredible highs."