Re: Secrets...
Yes you have to be honest. No doubt, but you always have to remember - HOW you say it also playes a big role.
If you just throw it as a shock, then a shock just may come back to you. I am not sure how is your relationship. you can ask them to come to the doctor for a regular checkup and discuss these issues there. Basically, find an easy way to let them know of FACTS (or potential facts).
btw, sometime too much honest it NOT a good thing :)