Sai is just laying like a stringless puppet while Shisui makes wonders with his mouth. He suspects than his current state is not because Shisui's ministrations -as heavenly as they feel- but to also what he's feeling for the Uchiha.
He's in love with him and he haven't told him before.
When He was on his mission that idea crossed his mind countless of times: Why I haven't told him I love him?
He thinks on the curls on shisui's head, who made him look innocent yet knowing how perverted he can be, those eyes with long eyelashes, deep enough to make him shake on his dreams, he thinks on Shisui's lips, now licking and hugging his cock greedy,how he can say such sweet words and make hot caresses.
"Shisuiii..." He half moans at the sight of his Uchiha "I can't take nnnhhggghh t-t-take it anymoooore" he bites his lips when Shisui looks at him, straight on his eyes and says to him he's allowed to cum "Shisui.. Shis-s-ui!" he screams when his clmax hits him, making him fall on the bed soundly, still breathing quickly and erratic.
While he's laying, he caresses Shisui's cock lazy, enjoying the faces he's making "Now, let me satisfy you, Shisui" He stands a bit and kneels on the bed, making the Uchiha now lay on the bed. He muzzles his cheek against Shisui's cock while he whispers "Let me do it, you don't know how much I wanted to suck you off" He looks at the eyes of Shisui and adds "three months. Three months dreaming of you, of no one but you".
He stands from the bed and kneels in front of Shisui, with his head on the Uchiha's crotch "I always wondered why I never toled you before" he looks at Shisui, who seems a bit stranged.
"I love you" he says smiling at him "I don't know if you feel the same but, for now, just enjoy my devotion" he keeps smiling, quite calmed and happy, "Just let me show it how much".
The mouth descends to the hard cock slowly, enjoying the growls and moans from the man he loves, he places his hands on Shisui's legs and makes his tongue to play with the tender skin near Shisui's crotch, nibbing sometimes -and gaining q satisfied sound, so Sai keeps doing it from time on time.
He stops his treatment with his tongue to add "It doesn't matter if you don't feel the same, just let me enjoy this moment with you" he ends and breathes deeply over Shisui's cock, now licking the tips of it.
Sai doesn't care if Shisui ends up hating him once this is over, as long as he can stay besides Shisui just this time.