You get that sense, that feeling at the very beginning when Mrs. Twist steps out the house to meet Ennis. She knew who he was, and what he was to Jack, and met him, not waiting for him to come to the door, or waiting for the knock, but meets him as someone important that comes to visit you at your home.
Even when Old Man Twist makes mentioned of Randall, she knew better, and told Ennis he was welcome to go to Jack's room. There were two emotions at work in this one scene, deep love and bitter disappointment, a battle for the memory of Jack between mother and father expressing distinctly how they felt about their son, to someone both knew was his lover.
Ennis got the sense of both people, this was Jack's world, something I don't think he ever really understood, or thought much about, not the way Jack understood him.
Jack didn't come to manhood with a "Rich or Earl" looming in the back of his mind, Jack grew up torn between the two people who raised him. Caught between brutality and love, with Jack choosing love and seeking it, and wanting it and giving it all to Ennis. When Ennis found the shirts he was just beginning to understand his long time lover, for these shirts was from the first summer, not after the reunion, but from the very beginning, Jack loved him then, and loved him till his death. And through it all Mrs. Twist knew and honored it.
Ennis had to feel a sense of relief, that someone knew and took pity on him.