Sensual Massage is focused on the actual touch of the skin. Stimulating the skin and the senses. It may be very soft, or firm. It may excite and even turn you on and it may include a happy ending. But its goal is to stimulate and soothe.
Therapeutic Massage is focused on the muscle and tissues underneath the skin. It includes many portions of the sensual massage, but it is focused on moving the muscles, breaking down adhesions, stretch, increase the range of movement and enhancing the body fluid movement. It may turn you on and it may or may not include a happy ending. But its goal is to relax.
Erotic Massage is focused on erogenous zones and turning you on. It is meant to stimulate your awareness, instead of your skin. Your skin may be stimulated, but the focus is on increasing your awareness and sexual presence. It may include stroking your cock or edging you. It may include your nipples, nape of your neck, hands, feet, ass, taint, cock, or anything else that may turn you on and heighten your senses. It is usual to expect a happy ending, or use it as a prelude to something more sexual. A happy ending is not unusual. But the goal is to turn you on.
It more blunt terms... sensual is rubbing; therapeutic is massaging; and erotic is foreplay.
Just my tuppence.