Gellert's teeth clenched when Albus pressed fingers into him, a sharp spike of pleasure that he knew was mostly psychological twisting in his core. Albus's demand that Gellert not call him 'professor' only confirmed what Gellert had already suspected -- that his conscience would be the primary aspect to appeal to later, when Gellert wanted something from Albus...or simply wanted a bit of entertainment. Gellert had, of course, slept with people far older than him than the gap that existed between himself and Albus (the deputy Headmaster, for one), but as far as he knew, Albus did not know that. And even if he had, Gellert had learned enough of the emotion guilt to know that even with that knowledge, Albus would likely find it impossible to rationalise his actions to himself.
The goal of sleeping with Albus, of course, was not at all the same as why Gellert had been with the deputy Headmaster. The latter had been for protection. Albus was...information. Gellert would probably not even need to apply extra pressure to Albus's sense of virtue to get what he needed. And what he needed, was for Albus to feel close to him. Beholden to him, in a way. To reignite that connection that might allow him to tell Gellert...everything.
And, of course, Gellert slept with Albus because he simply wanted to.
One of Gellert's hands jerked back, grasping the back of Albus's thigh as if to pull him closer, before releasing him to spread his hand flat against the table once more. Albus's fingers were long -- long enough to be perfectly, blindingly delicious. Gellert realised only after a moment that he had been grinding against the edge of the table, desperate for any kind of stimulation against his cock.