You reach a point where you stop trying - where you get tired of being the only one making an effort. And the sad part of it is that other person doesn't realise your absence. They don't notice your exhaustion, and having had you take the reins of the relationship, they don't attempt to do the same when you retire. They let things be as they are, and that only confirms your worst fear. That you were alone in that relationship. That you carried the weight of it on your shoulders, while they just existed - they just reaped the benefits of your love, and never dedicated themselves to nurturing the connection you thought you shared, the way you did.