Do you miss her body? Her breasts? Her ass?
At first open a photo of her which shows her clothed breasts.
Have a look at the photo, but don't look at her breasts, because they are not for you anymore. Look into her eyes, look down, or look somewhere else, but don't look at her breasts. It is not appropriate to stare at the breasts of friends or strangers, only her new boyfriend is free to look at her in any way he likes.
Now say out loud "I love and miss your beautiful breasts" and stroke your cock 50 times.