Definitely tell the truth and let her decide how she would like to proceed.  I've had this situation before with a client, and I chose to cancel, mostly because I can't imagine not kissing.  If you're upfront about it, it wouldn't really be fair of her to be upset, IMO.

and keep you from getting another outbreak. Cold sores are contagious and spread very easy. I would want to know and very glad you canceled.

First off there are a few product to google

BHT --- cold sore   very strong antiviral and good to always have on hand ----I like the "now" brand which is family run and owned with good reputation.

Olive leaf Extract ----cold sore ---- been taking this for 25 years during flu season and never get sick --- years ago I thought this could actually fight HIV and maybe cure it

Colloidal Silver  (ASAP  gel by American Biotech Labs )----- cold sore ---- I have 20 tubes of this on hand and brush my teeth with it after oral. With the product I suggest it is a gel and as soon as you feel the tingle  start putting it on the spot. It will dry the liquid up inside overnight but the small scab will need to heal and drop off. No big messy ones will arrive as long as you keep putting it on till it's healed.

Lysine --- cold sore -- This last product is actually an amino acid and should be taken daily so you won't have another breakout

Took some time to put this up so hope it helps someone

Kisses Haley  

Many ladies would still be willing to see you, of course without any oral contact (kissing or otherwise) from you though.

Just a suggestion, if your regular physician is aware that you get cold sores from time to time, you can ask for a prescription for Valtrex for that reason.  It wouldn't be like a regular 30 day fill, just a couple pills. You take one when you first feel it coming on and another 12 hours later and if you are lucky it may not pop up at all. If you wait until it starts to erupt, it will still reduce the healing time better than something OTC like Abreva. Usually no more than 4 days.

Cold sores = Herpes.

Extremely contagious from the first symptoms until the lesions crusts over which can be 7-10 or more days later.  Plus many people with herpes shed virus even when asymptomatic.

Remember, the if you touch your mouth you can spread the virus anywhere for example lips to fingers to other body parts on you or someone else.