He first realised he was attracted to Draco Malfoy at the end of third year and it was all Hermione Granger's fault.
The mudblood slapped him and from what Blaise can make out she probably had good reason. He can't be on her side though as even though she doesn't know it she's responsible for this predicament they are in. Through the snore of Crabbe and Goyle Blaise hears noises. He knows those sounds. Someone is wanking.
"Fucking mudblood who does she think she is? How dare she touch me? Etc etc" Blaise hears. He sighs maybe not then. He listens more to Draco rant.
"Powerful, beautiful, smart but dirty so dirty fucking mudblood," the rest of the sentence is a moan.
Draco Malfoy is wanking over Hermione Granger.
Blaise sits up his own cock hard at the thought of what Malfoy is doing. He sneaks over to Draco's bed not prepared to lose this opportunity. He throws back the curtains to reveal a very naked Draco covered in sweat. Blaise timed it perfectly throwing the curtain open as he comes up his chest with 'Hermione' on his lips. He opens his eyes looking up at Blaise.
"What do you want?" Draco asks realising his mate now has the perfect blackmail material.
"Admit it. Admit you want to fuck her?" He says.
"And you'll keep quiet?"
"Oh no I'll need more than this," Blaise tells him. "But first I want to hear you say the words."
"Fine. Yes. I want to fuck Hermione Granger," he says shiftly uncomfortably.
"Good boy first step is admitting you have a problem," Blaise says.
"What do you want?"
"A few things. First stop closing the curtains properly around your bed I want to opportunity to watch you wank. Second stop giving her shit every time you see her. It isn't necessary and you know it. Third I want three favours I will ask you for before we leave school for good and last but not least if for some reason you one day manage to fuck Hermione Granger is want the opportunity to watch."
Draco stares at him open mouthed. Before thinking it over. It would destroy him if this got out.
"First one fine but don't stare and we never talk about it. Second fine whatever. Third what sort of favours?"
"Non-sexual. Nothing that will risk your life or destroy your reputation," Blaise says.
"Done. As for the last one it will never happen," he scoffs.
"Then it shouldn't be a problem to agree to it," Blaise grins holding out his hand. Draco shakes it before realising his own hand still had some of his cum on. Blaise licks it off as he walks backwards to his bed. Draco pulls the curtains mostly shit leaving just a sliver as Blaise laughs.
Their relationship changes after this. Draco rants to Blaise every time they are alone about Hermione. He stops pretending around him that he can't stand her. He lets Blaise watch.
Two of the three favours come and go.
Once fifth year rolls around Blaise starts to push his luck. Coming on to Draco knowing he'll keep saying no but he just can resist.
His attempts at seduction become more and more ridiculous. At first he just starts wanking while Draco does so every time Draco looks up Blaise is there cock in hand.
Then begins the shower interruptions. Standing there as Draco showers stroking his cock.
"No Blaise," he gets told more exasperated each time.
For Christmas each year Draco finds Blaise on his bed naked expects for a bow.
"No Blaise," is the response every time.
After a partially gruelling Quidditch match Draco stays late in the showers. When he feels hands start to massage his back he looks over his shoulder.
"No Blaise," he says without much conviction. His back is sore.
"Just a back massage between friends?" Blaise offers.
He may have been in with a chance had he not chosen that moment to cup Draco's arse.
"No Blaise," is the response much more firmly.
When Hermione's boggart ends her relationship Blaise stops trying. He's more interested in getting Granger in Draco's bed than getting there himself.