"Where Are Ü Now (Marshmello Remix)" by Skrillex, Justin Bieber, and Diplo explores the theme of longing for someone who is no longer present in the singer's life. The lyrics convey a sense of deep vulnerability and the yearning for emotional connection.

In the song, the singer reminisces about the past, mentioning how they provided support and love to the person in question. They use imagery of giving someone a key to a door and giving them faith to symbolize the effort made to facilitate a strong bond. However, the recipient of their affection seems to have disappeared when the singer needed them the most.

The repeated question, "Where are you now that I need you?" reflects the singer's anguish and frustration. They feel abandoned and are seeking answers as to why the person they relied on is nowhere to be found.

The lyrics also highlight how the singer went above and beyond for this person, giving them attention, warmth, and understanding while others neglected them. This further amplifies the feelings of betrayal and confusion. The allusion to being on their knees in prayer suggests the intensity of their devotion.

In essence, "Where Are Ü Now (Marshmello Remix)" delves into the complex emotions that arise when we invest deeply in someone only to be left wondering where they have gone when we need them the most. It captures the raw vulnerability and emotional distress that can occur when relationships break down or when someone we care about seems to vanish from our lives.