The best way is to not forget them. Instead, work on accepting that they have the right not to reciprocate, and use your love to let them go. Deliberately turn your thoughts to your own life and your own future, and don’t let yourself dwell on them.
If you are having a very hard time letting go, try volunteering at a food bank or animal shelter or something. Helping others is a great way to feel better about ourselves and have something to look forward to.