In the scene, Alec comes to Magnus' door and tells him that he wants to take the "sex step" with him. Alec kisses Magnus, but Magnus isn't that into it: he tells Alec that he's afraid of losing him if they move further physically. Alec insists to Magnus that they have nothing to worry about because Alec now knows he wants to move forward. He then kisses Magnus and pushes him into a bedroom, presumably to have sex — without getting any sort of verbal agreement from his partner. Watch the scene below: