And that's Mako's fault? Mako wasn't drinking the Kool-Aid and he got to the bottom of it before anyone, nobody listened, including his girlfriend, even when he tried to talk to her rationally.
IF that were even true about Opal, the fact remains, she didn't explain this to Bolin and held it against Bolin for not knowing what she did when she was in a position to enlighten him. It wasn't that Bolin didn't listen (like Korra in the situation with Mako), it was that Opal wouldn't talk to him.
I'm not saying Bolin handled things perfectly, but he did deal with things far better than she did given the circumstances. It was childish to fake the injury, however, she wouldn't even discuss things with him. He was trying to open the lines of communication again, lines which she had severed. Really, she created the rift between them and had all the power to end it, even to have prevented it in the first place.
That's completely asinine and you should know that. The show is trying to beat into our heads (albeit poorly) that Kuvira's bad, Bolin is a stooge, and Opal's right about Kuvira the whole time, culminating in Bolin needing redemption. Opal is actually being a crappy relationship partner, however, the narrative seemingly attempts to lead us to believe that she is justified because she and we know that "Kuvira's bad." "That scene," I'm assuming you're talking about Bolin and his ill fated picnic/injury, frankly, should further drive home the point that Opal's the problem, because Bolin is trying desperately to get her to talk to him and repair their relationship, but she won't have any of that and this stems from her knowing something that he didn't know, she didn't even seem to try to explain to him, and she makes no attempts to mend the relationship herself, despite his attempts. Sure, that's certainly her right to not want to be with him, but it's really shitty of her to hold that against him when she could have prevented the whole conflict or at least given him the information to make an informed decision (if she herself ever even actually knew to begin with), then she could have justifiably been angry at him if he still opted to remain with Kuvira.
Except, you were flat out rationalizing:
By the way: in both cases, the girl being angry was entirely justifiable. Korra was eighteen and sheltered and had the figurative weight of the literal world on her shoulders, and Mako was being Mako;
Korra being young, sheltered, or having to deal with the stress of being the Avatar isn't a direct connection to the point of contention of her and Mako's disagreement on the Water Tribe Civil War nor is it even fair of her to take that out on Mako, it isn't Mako's fault she's the Avatar or that the war is going on. He tried to be supportive and was trying to (and eventually succeeded) get to the bottom of the plot related to it. Also, for that matter, he's just about as young, while not sheltered, he had to raise himself and his brother as an orphan without a loving home with people taking care of him, and he has a stressful career, why don't you cut him a break too? Like I said, I could empathize or understand why she's stressed out, but it doesn't make her subsequent actions right or even reasonable. It's not okay for her to pull a stunt like when she busted into Mako's workplace, started arguing with him, and flipped a desk.