So descend into cliché
If you've found your holy grail
For the first two lines, online sources will talk about succesful artists finding their thing (their holy grail) and then becoming cliché, but they don't really talk about what it means. Since Will refers to relationships and his ex as art often, I think this means that in this context, Will's "holy grail" is the break-up. It's what this whole album is about, so it's literally his artistic inspiration. But now, almost at the end of the album, Will has gone through all of the emotions a lot and these have now become cliché to him. He falls in emotional repetition and he now acknowledges this, but he isn't emotionally over it yet, so he descends into cliché. He's still feeling all the feelings.