After a minute: "Ah, Lan Zhan, I love you so much." 

"I love you." Cuddlesqueeze. Cheek kiss. "My Wei Ying."

"My Lan Zhan. I have no idea what I ever did to make you feel this way but I want to do it again and again forever."

"You do it every moment of every day."

"Lan Zhaaaaaan," he says, burying his face in the other's shoulder. "You keep saying things like that!!! It's ridiculous, you're so sweet, I wanna marry you." 

His ears blush. "Will you?"

"Yes, absolutely, under any and all circumstances." 

"I love you so much, Lan Zhan. I never want you to let go of me again either." 

"I will not." Kiss. "When we marry I will carry you everywhere."

"How is it that you can say things like that and I'm the one who's shameless???"

"I am being entirely reasonable."

"I'm reasonable!!! Nobody could not say the things I say with your mouth on them. Partly because nobody else gets to have your mouth on them ever but that's not the point." Maybe if he kisses Lan Zhan long and hard enough immediately after saying this he won't have time to disagree. 

This is a pretty effective strategy, well done.

Also it involves kissing Lan Zhan which is great!!!

Oh hey they're currently A) naked and B) in teenage bodies with teenage hormones. 

Perhaps their teenage bodies should now be: on top of each other.

Even Wei Ying cannot talk while having the breath kissed out of him (yet, growth mindset) but that doesn't mean he can't be VERY EMPHATICALLY APPROVING in his vocalizations. 

This is acceptable.

Having sex makes words even more of a challenge than usual, but Wangji eventually channels most of his concentration into articulating, "You are - very beautiful," between gasps. It's just very important that Wei Ying is aware. "Love. Love you."

"Ah, Lan Zhan, nobody is more beautiful than you," he gasps. "Love you, love you, so beautiful, my Lan Zhan."

...praise has some immediate and noticeable results.

Wei Ying is very in favor of those results. 

"So beautiful, so good to me, you make me so happy, I can never look away from you." 

a  a a. a.  a a a aa a a

He comes too fast, because of course he does, but Wangji reapplies himself to pleasuring Wei Ying as soon as he's aware of his body again.

"Love you," he pants into Wei Ying's neck. "Love you, love you. Mine."

"All yours, yours forever, never been touched by anyone else, never want to touch anyone else, love you, Lan-er-gege, oh you touch me so good,"

Wrists can be pinned out to the side. Neck can be marked. Very marked.

"Shameless," he whispers. "My shameless Wei Ying. I will touch you forever."

He whines, high and deep in his throat, head thrown back like Lan Zhan having less than optimal access to his neck is the worst thing imaginable.