That said, some additional ideas on Susan and Roland. There's an interesting phrase in W&G: She needed to see him at his right size, instead of the one her mind had created for him in her warm thoughts and warmer dreams. W&G/On the Drop/Chap VII/ Sec 6/p258

First time or two through with Roland, I saw him as a giant--he could do no wrong--wadda ya mean he dropped Jake!--that kinda thing. Maybe that's a problem. Maybe if we didn't see him as a giant, a hero that can do no wrong.

For instance, perhaps his fatal flaw is his inability to forgive Gabrielle, that leads, in part, to an obstacle to love. His old man talked to him, Steven spoke about many things over the whore’s bed to Roland. “About Roland’s mother, who was, perhaps, more sinned against than sinning.” W&G/Long After Moonset/Chap IV/Sec 1/p170

An interesting phrase, from King Lear, fwiw, but why does Steven think such a thing? Wasn't he the one wronged?

Later, on the Drop with Susan, during the blood kiss moment, Susan tells Roland: “If you really do love me, don’t let me dishonor myself. I’ve made a promise. Anything might come later, after that promise was fulfilled, I suppose…if you still wanted me…” wg/vii/9/270

They kissed again and she stepped forward.

“She was, at least for the moment, no longer her own mistress; she might consequently be his. He could do to her what Marten had done to his own mother, if that was his fancy.” Wg,vii/9/270
“The thought broke his passion apart, turned it to coals that fell in a bright shower, winking out one by one in a dark bewilderment. His father’s acceptance.
(I have known for two years)
was in many ways the worst part of what had happened to him this year; how could he fall in love with this girl—any girl—in a world where such evils of the heart seemed necessary, and might even be repeated?”

So he obviously saw Marten in himself, yet it didn't stop him. Ka, like a wind.

I think it was interesting, in The Wolves of the Calla, that Roland tells Susan:
spoiler


Maybe the quote helps understand the custom. Maybe not. Shrug. Perhaps there's a message there, as well, for us, the readers. Like the first time through, I saw giants. They could do no wrong. Maybe, like Susan, we need to step back and as King wrote:

"She needed to see him at his right size, instead of the one her mind had created for him in her warm thoughts and warmer dreams." W&G/On the Drop/Chap VII/ Sec 6/p258

Anyway, I'll hazard it again, that there is some kind of doubling going on with Roland and Susan's actions, kinda like Marten and Gabrielle's. Are they exactly the same? No. Not saying that, but Roland did see himself as Marten. The question is, is his fear of love a contributing factor in his choice of the Dark Tower over a life with Susan:


“Inside the ball, I was given a choice: Susan, and my life as her husband and father of the child she now carries…or the Tower. Roland wiped his face with a shaking hand. “I would choose Susan in an instant, if not for one thing: the Tower is crumbling, and if it falls, everything we know will be swept away…As for me, I choose the Tower.” W&g/x/beneath the demon moon/sec 10/p605