You should tell them soon, but not right away---don't let stigma and social cliche's wrap his idea of what your condition is....however, don't hide it. Just bring things up a bit casually and don't get too heavy about it.

If you got anxiety, just say you have anxiety. Once you know him well enough, you can slowly let him into your mental world, just make sure you don't tell him things you wont want others to tell you about their mind .

TO be honest, even though my friends know Im a good person and I won't do anything terrible, my OCD gives me strange ideas, and I know it's best for all my relationships I don't share it---and I just take it straight to at therapist. ( have yet to get one, but thats my plan).

There are some things that are just a bit awkward or seem inappropriate to share (like for example, I hear women really dont want to know whats on a man's mind---and it's best not to...you don't want a guy to share every detail of how he thinks about you, or other women around, females in movies, or his fantasies--you probably will get freaked out too!)