Spoilers for the end of season 1 & the first two episodes of season 2. Everything else is made up. This is my first foray into the Grimm fandom, so please be gentle.
Nick is crushed, and Monroe doesn't know what to do. He is always the first person that Nick calls when he needs help, but this isn't a regular case. This is Juliette. The love of Nick's life, the woman that Nick planned to marry someday. Monroe desperately wants to fix Juliette, but he can't do anything about her memory loss. He and Rosalee tried, but they couldn't get to Juliette in time, and now, Juliette doesn't remember Nick. She doesn't remember anything about their life together. Monroe can't imagine the pain Nick feels and how heartbroken he is. He was sleeping when Nick showed up at door in the middle of the night, unable to speak from crying so hard. Nick hadn't asked to come in. but Monroe had allowed him to. He hadn't said anything when Nick collapsed on the couch, curled up in the fetal position, sobbing. What could he say? All that Monroe could do at that moment was be there for Nick, just like Nick would do for him.
"What if she never remembers me?"
"She will. She's gonna be okay, Nick. I know it."
It's not entirely the truth, but it's all that Monroe can offer right now. This seems to placate Nick, and when Monroe comes back from pouring himself a glass of water in the kitchen, Nick's asleep, his breathing slow and even. Monroe regards his friend with a look of concern one final time before he leaves the room and makes his way to his bedroom.