Sweet - Nothing more physical described in the book than handholding, brief kisses and embraces. Limited displays of affection.
Warm - A step up from sweet. Prolonged, sensual contact. Longer, deep kisses. "Making Out." Sexual intimacy may occur, but description goes 'to the door' and stops. No details.
Sensual - All the heat, all the build up. Deep, heart pounding kisses. Desire. Physical need is apparent and obvious, spoken of between them. Physical intimacy is likely, though not guaranteed, and would be described in allusion or implication, not details.