Ask yourself: how much is pain gonna give me? How much will it cost me if I die today without the person and she goes on to enjoy her life without still giving a damn about you? At end who lost? You.
Actually it not you "can't" but you "don't" want to let her/him go. Yes, it very hard to do but oftentimes you must. I will stay away from her presence, shut my curiousity about her (Facebook/social media) and never contact her anymore.
