Okay. Let's define "nitpick": From the Oxford English Dictionary -
look for and criticize small or insignificant faults or errors
Is the relationship between Book and Burnham small? No. The way it's handled is intrinsic to their character growth. And to have them break up off-screen, then get back together again with nary a cross word between them is absolutely more than a nit to pick. It's the same problem I (and MANY others) had with the Seven / Raffi relationship on PIC, and to a lesser extent the Gray / Adira relationship (Though I didn't complain as much because I was glad to see Gray gone).
It represents a problem some of these writers seem to have: They do not know how to write real relationships, with real problems that come up without either side being a "villain". SNW has handled it pretty well, with Pike / Batel, and also Spock / Chapel / T'Pring. But Picard and Discovery both really, REALLY struggle with writing dynamic, compelling relationships where everyone's not happy all the time. And that's not a nit.