"That's why I shouldn't allow it"

In the episode 256, Serpico said.

Madam Farnese isn't the only one that has been changed, I've also changed much myself [...]
I've felt helpless with the fact that Madam Farnese has been changed beause of you but I've also been happy with that.
That's why I shouldn't allow it.

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I thought much about that but couldn't figure it out.
Does it mean that he shouldn't allow it because Farnese has been changed because of Guts, or he has also been changed? Or because he's felt helpless but has also been happy with that? Or because of both reasons? Or another one? ???

Miura said this in an interview with Kurimoto Kaoru (栗本薫) in the Guin Saga Official Navigation Book.
It's not sure if Serpico is such a character going toward a life for the other only
I think we can see well what Miura said in this episode.

All we can know clearly is that Serpico doesn't want Guts to kill/hurt Farnese. But why should it be related to his lines above?

I believe that Serpico is happy with the way Farnese is changing, he even says so, but he "shouldn't allow it" because he wants to be the one to change her. Just a selfish, pride filled, me me me thought. :)

- C

Perhaps Serpico is more conflicted about his own roll and reactions than Farnese's. だからこそseems to refer specifically to his contenment with Farnese changing, so maybe he feels like he shouldn't be admitting this positive feeling. If he feels alright about how Guts affects her (and him) then that would cause him to want the two of them to join the group again...leaving open the possibility of Guts killing Farnese when under the influence of the Beast.

Maybe?

Maybe he was trying to say "He wouldnt allow the man who changed her kill her in the end?"