I'm 38 and just realized I'm a lesbian. How do I handle this??

At the tail end of pride month, it kind of slapped me in the face, oh no, I'm a lesbian. I've identified as queer for most of my life, having settled on biromantic/asexual as my major identifiers for the past 15-20 years. I was happy with that, and I have been happily and monogamously partnered with a man for 12 of those years. We raised his kids as a family, and all together, they are the loves of my life.

These kids don't have a bio mom. If my partner isn't my best friend anymore, then who will I be to them? How could I possibly go on without them? They are older (youngest will be 17 soon), and 2 out of the 3 of them are LGBTQ+ as well, so it's not as if they wouldn't understand, but they've already been through so much, and their relationship with the role of "mother" is so strained already.

This is to say nothing of my man, who has supported me and loved me for those 12 years. I know it isn't fair to him to live a lie right in front of his face, but is it fair to destroy what we both thought was gonna be forever either?

I'm so confused and hurt and I feel like I've betrayed myself. How am I gonna get through this? How do I tell the truth without losing my family?