I think Yuvraj went into shock or semi-shock bec even after Gauri admit she did it all as revenge...he couldn't believe it...so I think the issue is that he just cant believe someone, esp someone who's his own blood would destroy someone in such a cruel, cold, and heartless manner. Up till this point he'd been shown disregarding Gauri's violent tendencies so I think that was a hint that he doesn't think his sister is dangerous. He's living in some serious denial or maybe the weight of it has just blinded him totally. He rly didn't think Gauri could do this so I think he's probably shattered, hence the denial even in the precap.
I also feel that Yuvraj supported Suhani in this from day 1 if not by his presence then by emotional support. He never doubted Pankaj, not even for a second. That's a big deal in itself and he was all alone and stood by her and against his family. That was him all this while, not Saurabh & Sharad. Not for a second do I think that he wont be repenting for his harsh words today...I think that regret and repentance is what's next. I do think they'll be separated.
IDK, I don't feel Yuvraj was completely wrong bec I think he truly thought Gauri is incapable of such wicked plotting...and now he knows the true nature of his sister. Those blindfolds have been removed permanently. I do think Yuvani will be separated now bec some wounds don't heal. I never wanted Yuvraj to be perfect and frankly I thought everyone wanted a separation and was waiting to see their mutual trust take a hit and that's what happened today. Today we just found out that he doesn't blindly love Suhani. He isn't some demi-God or utterly perfect husband and I never wanted him to be. But I do think that they're love is strong enough to overcome all of this, especially his bec I think he hurt her today with his words and he probably hurt himself as well...bec I still believe that's how deep his love is. Just because he didn't believe her today doesn't mean he wont believe her tomorrow.