Unwritten Rules (The Savages of Falcote #1)
Ally Hastings

No one ever pays much attention to Lucas Greville. His brother manages the estate, his mother is preoccupied with finding husbands for his sisters and the cousin who promised to show him around London abandoned him at the first opportunity. He is not an attractive match for girls on the lookout for a title or a fortune, and he fully expects to spend his first season in cheerful anonymity.
When Richard rescues Lucas from an unpleasant situation at Greene’s it is the start of an entirely proper friendship, and neither of them is looking for more. But then a stray word from his new acquaintance sheds light on the great mystery of Richard’s life. Can Lucas help him discover the circumstances of his birth? And will the resulting upheaval help or hinder their growing affection for each other?