I've just pinched this ......
"I think Thomas has resigned himself to the fact that an epic love story with a man isn’t going to happen for him, any hope he had for that rode off with Jimmy Kent. He possibly believes that in the confinement of servitude, the society and time he lives in, that his best chance of happiness/normality would be to try and settle down with a woman. He sees Molesley and Baxter developing something, he hears Anna and Bates whisper about having a baby (even Jimmy getting some action, despite the disastrous outcome) and he envies them enormously. He’s been alone for so long and he’s probably sick of his love being unreciprocated and being celibate for years on end."
That was good link Robinia, but video was just buffering for me :(
The word "on the net" seems to be that it's heroin he's dabbling with, silly boy!