headcanon: James tells Thomas that he cherished that one special copy of Meditations during all those years they spent apart, but he lost it at some point in the war. So Thomas now writes things for James in all the books they own, from the most poetic love-declarations to just random silly notes and inside jokes.
James. Every day I wake up next to you is the best day of my life.
My truest love. Thank you for doing the dishes.
The little chickens!