Since this hasn't collected an accepted answer yet, I'm going to suggest another possibility might be The Jargoon Pard (1974) by Andre Norton. It's definitely a young-adult novel, with no overt gore, sex, or gratuitous violence.
The hero, Kethan, is nominally the heir to the keep Car Do Prawn, but in this he is supported only by his mother Lady Heroise and the Wise Woman Ursilla, who seeks to control both Heroise and Kethan to her own ends. He is opposed by Maughus, his cousin, who would be heir were Kethan disqualified, the Lady Eldris, his grandmother, and other lesser members of the household.
The Lady Eldris arranges things so that Kethan is gifted with a strange belt brought to Car Do Prawn by a trader named Ibycus. The belt, made of the fur of a pard and set with a jargoon stone, awakens an animal spirit in Kethan. (A pard is a large solitary hunting cat, larger than a dog but not so large as a tiger.) His mother warns him about it, but desiring to be free of her power and based on something Ibycus told him, he keeps it on. After a couple of days of vivid dreams, it transforms him into a pard. At first he can transform back by taking it off, but because of Ursilla's machinations he becomes stuck in the form of a pard just when Maughus bursts into the room, revealing Kethan as a Were and unsuitable to be heir.
Kethan flees and discovers a trio, man, woman and daughter, living in a star-shaped tower of ancient and great Power deep in the forest. The girl, Aylinn, has a talent with the Power and an affinity for the Moon, and he first meets her collecting collecting moonflowers by moonlight. After first being turned away, becoming trapped and needing rescue, Kethan is brought to the tower. He stays with them in the tower a short time while they heal the wounds on his back that Ursilla's hawk inflicted. The man, Herren, is also a Were, with the form of a snow cat, larger than Kethan's pard.
Kethan, healed, leaves to seek an end to his curse by regaining the belt that Ursilla has stripped from him. A series of escalating confrontations with Ursilla ends with her destroyed, Kethan renouncing any claim to Car Do Prawn and joining with the trio as Ibycus reappears to tell them that the four of them together now have a greater role to play in coming events.
The only thing that doesn't really fit is the romance aspect. Yes, at the start Kethan is betrothed to Thaney (his cousin), but there is no love there. There are hints when Kethan meets Aylinn that he might be attracted to her, but those are understated and their interactions aren't romantic.