His hate for the Agrestes is so deep that he impersonated Adrien and made a hateful video call to his friends on Adrien's tablet to destroy his reputation with them, even though it was a pointless act of cruelty that did not help his primary goal of stealing the wedding ring at all.

Does Felix care about Adrien?

Félix might harbor some kind of jealousy towards Adrien as he was surrounded by friends while Félix was alone. He also called him an idiot. In "Risk", he pretends to care much for his cousin.

Who is Felix in love with miraculous Ladybug?

Marinette Dupain-Cheng/Ladybug

When Marinette is Ladybug, Félix romantically pursues her.