You'll find yourself chasing after a ghost at least once in your life. That is someone who was never truly there. You thought they cared about you. The only thing that was ever real is the affection you felt towards them. In every other possible way they were absent from your life. They do exist, of course, but in their own little world. You are not a part of it. Others are. Not you. You never were.
Don't bother chasing after some one. Don't you feel that exhaustion? You're the only one doing the chasing. And what does that mean? You aren't being chased, looked after, cared for. Leave them alone. After a while if they miss you they will reach out for you. If they don't they never really cared. Yes, the old if you love something let it go. Just don't let it be because they need something from you. It must be because they need you in their life, because it's just not the same without you in it.
If they don't care that you're gone, they are phantoms, never really a tangible presence in your life. And your life will be better without them. At least less exhausting.