I was diagnosed some decades ago and have been on meds since I was in my 20's (I'm now 57). I still have times of great doubt, panic, almost, thinking that I don't have a disorder at all and have been taking meds for absolutely no reason.
But then I stop and remember the times when I wasn't properly medicated and the reality, the truth, hits me all over again: This is real.
I have no spectacular answers. I have learned (finally) to take life day by day. Some days I'm stronger, some days I'm not at all. I keep a routine that suits my mental and physical health.
Something that has been quite helpful for me is watching films or documentaries about bipolar disorder. From those I obtain information and understand that I am not alone in this, not by a long shot.
This forum is a tremendous support. And giving feels as good, or better, than getting.
Therapy is essential, as is being consistent with meds. For me, support groups have always been helpful (before covid).
I think that anyone diagnosed with BD is, to one degree or another, in a slight state of shock. It's a very strange feeling, I think, to be diagnosed with a disorder that is so much a part of the essence of your Self.