[Buzzoff]

Do you intend to do it again? If you intend to go for massage and do HJ again, confessing it and saying sorry would be meaningless. If you really feel that you have 'betrayed' her and is determined not to do it again, then confession would be good and you will have peace of mind. Personally, it will provide yourself a closure of the guilt you are feeling. Definitely, your partner will be super duper upset (you have to be mentally prepared for this) but after that phase, she will appreciate your courage to be truthful to her. Well, utlimately, the choice is yours. Good luck.