You can't fit new love into a heart that's already full of love ... or something else, any more than you can fit a new wardrobe into an already over-flowing closet.
To the extent you want to welcome new love into your heart and life, you must consider letting go of all of the anger, hatred and homicidal thoughts you have for your ex.
My daughter is really upset with someone right now, and I was explaining to her today that forgiveness is an inside act. The other person doesn't even have to know you've forgiven them. You don't have to invite them over for Easter dinner, or spend hours on the phone with them, or even be more than cordial to them when you see them.