Genital herpes spreads by direct skin to skin contact with the affected skin. If a person has active genital herpes, there will be redness of the skin with blisters or erosions (broken skin) on the skin.
This is when the risk of transmission of the virus is highest if there is contact with the affected area.
It will not transmit through clothing but skin to skin contact, so if the masseuse was clothed when she sat on you, there will minimal risk of catching the virus.