How do I forget someone who meant so much to me before?

Hey, whatever you're going through must be so hard and some might not understand it.
What I recommend is try to do activities that makes you happy or relieves stress. You can vent to a journal if that makes you feel better. Communicate with your close ones and maybe they can help you through this time.
Or just spend time with yourself, and take care of yourself. Respect you and your body, or practice mindful breathing.
I really hope this helps you in some way of what you're going through. It might be hard, but give yourself time.