I knew someone who only committed his heart once. He had one pet as a child, and after that died, he never had another pet. Not that he disliked animals; he just wouldn’t have another to love and be responsible for.
While growing up, he took out different girls and women, none for any length of time. Then he met and fell in love with a woman. She was married at the time (vey unhappily and was abused). He rescued her and fell in love. They lived together very happily for many years. But then she left because he drank too much. He never got involved with another woman until he died.
He never had any children.
I sometimes wonder about him.
I don’t think he had a hard heart. He was a wonderful friend. As people said at his funeral, he was stubborn, and once he made you his friend, he’d never let go, you could always rely on him. But for the relationships that involve the heart in the deepest ways, for him, once only was enough.
I suspect he had a dreadfully soft heart, and that the loss of his one pet and his one love left him so bereft he could not face going through that again.