Poe knows he should hate Rey for what she's done. By running headfirst into enemy territory and handing herself over to Kylo Ren, she endangered everything the Resistance has worked for and undermined every achievement they've ever made. Snoke could have tortured her into revealing all their secrets, and then the entire galaxy's last hope would have been snuffed out in the blink of an eye. And even if she somehow succeeded in turning Kylo Ren, that would have opened another can of worms. It would have been a devastating blow to the First Order, yes, but most of the Resistance would have refused to put all that history aside to work with him – Poe included.
And Finn, in all likelihood.
Yet he can't truly hold the choice against her. He's taken countless risks in his life, some of which have paid off while others have blown up in his face in a roar of flame and blood. He never would have tried to turn Kylo Ren, but he's made other decisions that are equally risky, so it would be hypocritical to blame her for this one. Especially when she seems, he hopes, to have learnt from it.
So in the days after they return to the base after she saves them from the cave, when she fidgets and stutters whenever anyone brings up why she left and where she went, he helps her by changing the subject to something easier or giving her an opening to duck away.
If she stays with the Resistance long-term, she'll eventually have to front up to errors she makes and let the others hold her to account for them. But for now, it's better for everyone for her to be shielded from that.
A/N: Prompt: 'And mostly I hate the way I don't hate you. Not even a little bit. Not even at all.' from Ten Things I Hate About You