I think though too, as Queen hinted at, it's not going to be a total surprise to him if you bring it up. It's not like you're suddenly going to start being/behaving any differently than you have. You could start the discussion by just stating you have a medical problem and that it can influence your behavior but you aren't anticipating anything changing at the moment. Then let him ask questions if he wants.

I had a boss who was bipolar and thought it was a secret :-) but I had been coming to sites like PsychCentral and had mental health issues of my own so I guessed. Her daughter was diagnosed with it while I worked there (I worked at my boss' home, she had a couple offices in her basement) and the daughter was away at college and had not known about her mother's illness or that her uncle (father's brother so she got it from two sides) was bipolar and wasn't taking it well/believing she had it. I finally started talking about my own mental health issues in a compassionate, matter-of-fact way :-) and eventually my boss understood that it was "safe" to talk to me and tell me whatever she wanted instead of looking nervous when she said anything and hinting at dire things happening.

You can/are dealing with your illness, "show" that and be as open as you can and, if he's the sort of guy who is worth being around, he'll respond in kind and reassure you that the relationship can go forward.