"Kissing is good. — how much do you happen to know about how human sex works." 

"...nothing?"

...yeah, the amount that Sasha wants to give the talk to a fairy who is magically bound to obey his every order is roughly zero. "...actually, Marlo and I should probably talk before anything happens on that front. Sorry for bringing it up." 

"Okay." There should be more kissing. Leo is pretty sure of this.

There can be more kissing! 

Meanwhile Sasha is trying to work out where he and Marlo can talk such that he won't be neglecting the person whose well-being he's responsible for but also Marlo won't be too tongue-tied to do anything but agree to things he doesn't really want to agree to, but he can totally kiss Leo while he's doing that. 

Eventually Leo pulls away and says, "I have HANDS."

"You do have hands! And they have opposable thumbs on them!" 

"I can read BOOKS!"

He bounces. From what he has seen of school, books are even better than kissing.

— oh, that's an easy way to solve this problem. 

"You can read books! Some of them might be confusing but I bet you'd like them." The Shining is still on his bedside table from yesterday, A Face Like Glass is on the floor next to Sasha's desk, he can find a handful of books that Leo might like. 

"You okay if I leave you here to read while Marlo and I find somewhere and talk about the thing?" 

Leo has already started reading The Shining.

Then Sasha will take Marlo's hand and bring him through Sasha's parents' room out to the roof and sit with him there. 

"You okay?" 

"I'm okay," he says, and — can he safely lie down so his head is in Sasha's lap — yes he can. He does that. "...I don't love seeing you kiss other people but I think knowing you were doing it while I wasn't there wouldn't be better." 

He pets Marlo's hair, very gently. "Do you know what specifically upsets you about it? — I find monogamy really confusing, the reason I've been able to do it for this long is that I was basically not interested in anyone else, whether I keep kissing Leo or not it's a conversation we should have." 

"I..." 

Sasha keeps petting his hair, waits for him to figure out his words. 

"...I think I worry about whether I'm important to you. I know it's silly, but — it makes watching you watch Leo a bigger deal than it should be." 

"It's as big of a deal as it is, there's no should." He lets his hand rest on the back of Marlo's head. "I've only known Leo for a day. You're my commitment, I know you know that." 

"I do know that. — you've only known him a day and you're kissing him, though, that's the problem." 

"I can wait." 

Marlo opens his mouth, closes it, squeezes his eyes shut, swallows, opens them again. 

"...you waiting feels like the kind of thing I don't get to ask for." 

"You get to ask for anything you want. I could say no, but you still get to ask, and then I get to say yes." He leans down and kisses Marlo's forehead. (Right in the center, where his horn would be if he had one.) "I don't want to do things that make you worry. And waiting until I know him better is not a problem, it really isn't." 

"....I love you." 

"I love you." Another forehead kiss. "Ready to go back in?" 

"...I kind of want to stay out here with just you for a while first." 

"Okay," Sasha says, and takes Marlo's hand and squeezes. "We can do that." 

It's a while before they go back into Sasha's room.