I can relate to this a lot! I was misdiagnosed for 8 years as major depressive. Last year around this time I was diagnosed BP 2 with panic disorder. I started dating someone earlier this year and told him on our second date, just because I wanted to get it out of the way. He was fine with it and glad I told him and knew I was dealing with it, and he did his best to understand it. We have since broken up, NOT b/c of me and my BP.
If he knows about your other diagnoses, I can't imagine he would feel any differently about you b/c of this one. The stigma is there, so I totally get your anxiety about telling him, so if you do tell him, do it when you feel comfortable with it. It took me awhile to accept my diagnosis and I didn't start dating the b/f until 6 months later, so I had awhile. Do it when you want to and/if when you feel like you should.
Hope this helps. Good luck.