The first is that when Ennis finds his shirt in Jack’s closet, it’s inside of Jack’s shirt. But in the final scene, Jack’s shirt is inside of Ennis’.
Jack had Ennis inside his heart, all that time ago. He spent decades trying to get Ennis to embrace their true identities and their love, but Ennis was too afraid. But by the end, Ennis realizes what his fear cost him, decides to be himself and embrace Jack for the rest of his life.
The second is more subtle but more simple. Ennis’ only mementos of Jack are kept “in the closet”.
by King__Witch