This is a fun idea for a class that needs more work. The notion of a bold and brave cavalryman who laughs in the face of danger is a fun design. With that said, there's two specific gripes I have, and an overarching one.

1) What does having a mount do? What are the restrictions? What are the benefits? Can the mount die? What kind of checks do you need to make for the mount (does it check morale, for example)?

2) Being able to give yourself advantage on a Sworn Enemy is a nice idea, but is there a limit to being able to do this? Can I make a new enemy instantly after defeating another? Advantage is a VERY big boost, so being able to constantly apply it to a foe feels OP. At the very least, specify being able to do it, say, CHA times per day, and then the 2-talent adds to that count.

Finally, this class feels like it amounts to getting advantage as often as possible. Instead of encouraging a specific tactic or playstyle, it just puts the odds in its favour in more and more scenarios by just declaring it. Again, the theme for the class is cool. A bold knight with a noble steed who is compelled to strike down his enemies is a great fantasy. The gameplay mechanics to fulfill it now need to be fleshed out to be clearer and more nuanced to play with.

The term “willing creature” is doing a LOT of heavy lifting. Is ANY creature that is willing a mount? Like, elephants or giants or ancient old gods? Imagine a charger using Cthulhu as a mount. Perhaps “medium-sized riding animal” would be better.