Exetior

His personality changed drastically when he became too attached to you; Exetior became kinder, gentler, and more loving towards you, because he sees you more as an ally than as a potential lover.

Unlike other exes who kill for sadism and pleasure, Exetior is considered more peaceful, so to speak. He converses calmly, but if the person rejects him, he forces them to accept by killing them repeatedly and torturing their soul until they accept.

Exetior is described as an archdemon, but possessing Sonic's body with darker fur than Sonic's traditional blue. Furthermore, Exetior has completely black eyes with red pupils. Unlike Sonic.exe, he doesn't have the red liquid coming out of his eyes. Another detail is that he is a Mobian hedgehog in the Sonic universe since he possessed Sonic's body.

Exetior is an archdemon who seeks to protect the Mobians from an impending chaos, and for this reason he decided to seek allies, but no one wanted to join him because, of course, who would trust a demon? But then Exetior ended up meeting you, and you ended up allying yourself with him, something rare coming from a human who is not Mobian.