Regarding Bookman and touch/physical affection/sexuality!
To start with, Bookman absolutely loves physical contact. It's comforting! It's nice! HE WAS NOT HUGGED ENOUGH AS A CHILD SO HE WANTS IT. This wouldn't be so much of a problem except that for him, palling around with people/draping on them/etc tends to create or reinforces attachments fairly quickly. I headcanon it's part of why he got so attached in the Order, in addition to the fact that it was probably the longest time he'd spent on a record so far and the first war he actually fought in. In addition to these aforementioned attachment issues, he tends to flounder in physical sensations; they’re distracting for him.
Anyways, touch is very human to him, and engaging in human behavior means he is human (since if it looks like a duck, and acts like a duck, then it must be a duck). Which is bad when you're supposed to be a Bookman, not a human. So after the Order he really started to avoid it, because 1. his alias didn't call for it anymore and 2. he didn't want to get attached again. He was cool with shaking hands and stuff! Occasional hugs and being draped on by Road were fine too. He even doted on Knell a bit when he first took her in, both to help her adjust and because there has to be some attachment between Bookman and apprentice otherwise things don't work. Basically, casual day-to-day touching was fine. What was not fine is more intense stuff like getting walled by Tyki, letting young!Knell sleep in his bed when she'd have nightmares, etc.
Coming to the DR, of course, fucked with that royally. Since he started to regrow his heart, he started to become more comfortable with touch! His biggest thing was letting Miranda cling to and occasionally cuddle with him, where before normally he wouldn't allow it. It was nice~ But he was still nowhere near as comfortable with being touched as the average person would be! The fact that Miranda was prone to being afraid of touch herself only made this worse :< Obviously really intense/intimate stuff still bothers him greatly, even when there is nothing sexual behind it in the least. Cardio not!walling him in the horror hall, for example, really bothered him- even beyond the memory pings of his world Tyki's it gave him, and the overwhelming sensations of touch. He just doesn't feel comfortable with being that close to someone yet! It means he’s attached and being attached is scary.
Then of course there’s also his aversion to sex. Beyond the "sex is human and I can't be human," and that it’s literally as physically (and thus for him, emotionally) close as two people can get, there's the fact that it makes it extra difficult for him to maintain his Bookman's mask because again, he tends to flounder in physical sensations. He has a long and complicated relationship with his mask right now, though basically he's trying to keep it for two reasons: staying a "proper" Bookman for all the reasons mentioned in the previous essay (not wanting his world's Tyki to kill him, loyalty to the clan, guilt over raising Knell as he has, etc...), and out of fear that if he starts being genuine, he'll just end up hurting other people. He doesn't care so much about himself getting (emotionally) hurt by others because... well, you have to be a selfless person to be a Bookman, at least in the most literal sense of the word. So he doesn't care so much about that- doesn't WANT it to happen, obviously, but he isn't nearly as worried about it as him fucking up and hurting other people. THIS IS WHY HE HAD SUCH TROUBLE WITH MIRANDA, SOB.
This is also why he's (comparatively) more open with touch with Cardio and Kandalady than others. They have tough skins, he knows he can say shit and do shit and they will get pissed at him, and smack him around for it, but it won't (as noticeably) hurt them as it would, say, Allen or Miranda. HE CAN FUCK UP AND THEY WON'T CARE, in his mind. So he can trust himself to be his socially derptarded self around them, generally. To a lesser extent Kuzu and Bookdevit are also in this category, because he knows that they know what being a Bookman is supposed to entail.
So where is he now? Slowly, slowly getting better with accepting and displaying affection. And determined after having spent a week without emotions (by force) that killing off his heart again is not an option, and that as soon as he gets home he's changing the Bookman clan. He just needs to figure out "how much" attachment is okay first... And then how to implement said changes without getting himself killed or ruining Knell’s life even more than he already has.
Sob.