I used to only confide in one person but I think different people will understand and respect you in different ways and it may be good to try to open up to more than one person. That way you get different perspectives on things and also some people are better at listening, some are better at advice, etc.

I had a best friend who over the years has changed so much it's mostly not worth telling her about my current issues! It's pretty funny especially because now, after 12 years of being good friends, she lives three blocks away. But when I confide in her she doesn't see eye-to-eye with me. Our values have changed over time.