Is there a good way for me to tell my boyfriend about my bipolar disorder?

Be honest: Be upfront and honest about your illness. If he truly cares about you, it will make no difference and he will respect your honesty. If he is unfamiliar with the illness, suggest some ways he can get some education. Websites can be helpful, although people can present differently with bipolar. Perhaps a couples counseling session or doctor's visit could help as well.