Pretty much the whole episode was about how he DIDN'T know. And you're talking about this as if he had a choice in the matter. He didn't. So he failed with previous partner (who was booted out, and he was requested to stay) and suddenly he's supposed to know that he's not compatible with anyone else?
Which at the same time, unless I missed something, it's odd that they seemingly (even Naomi) weren't tested with others... unless their test as partners proved them to be failures regardless of who the partner would be.
That aside, it's all good and well to "know" you can pilot with someone, but what then? What if she's not available? Is it enough to know you're dependent specifically on this 1 person? You want him to grow balls, to get better, yet you seem happy to leave him complacent to being Zero Two's darling and that's it. What is it, should he aspire for more or not? If in the end Zero Two is all he'll have, so be it.
By the same token, if he'd gone all out "I ONLY PILOT WITH ZERO TWO" in that scene, to me he'd been made to look like a bigger loser then.
Yeah, he's been shown to be a crybaby at times, depressed in others, etc., etc.
I get your complains, but I think you're taking it a bit to the extreme.