My [39f] husband [38m] fathered a child before we were together and I just found out, 14 years later

After 12 years of marriage, and 2 children together, I received a Facebook message yesterday from a woman who told me that she has a 15 year old daughter that my husband has continually denied since her birth. The child was produced from a ONS and afterwards, my spouse did everything he could not to see his child. The mother eventually had his parental rights terminated and she moved away for many years.

Fast forward to now, my husband has buried this secret as deeply as possible. On the other hand, his daughter is now having some issues and her mother contacted my mother in law in January, imploring him to reach out to his daughter, threatening to tell me if he did not. Apparently they had a 30 minute FaceTime (which he lied about last night until confronted with evidence her mother provided to me and then he admitted that it was true) and then he blocked the account so she could not contact him again.

Her mother claimed she sent the message out of love and concern for her daughter, and I understand that she wants her to have a connection with her biological father. But she blew my entire life up in the process.

My husband has lied and lied and lied, even after confronted last night with hot evidence. He eventually admitted to everything, but only when backed into a corner. I asked him to leave the house last night so I could clear my head. But the truth is that I can't even look at him rn.

I don't think I've ever felt so dumbfounded, hurt, confused and betrayed all at the same time. My instinct is to call a lawyer to see where I stand, legally and financially, as I'm not sure I can continue this marriage knowing that I might never feel like I can trust him again. My family thinks I'm being rash bc I'm hurting SO much and this is 12 hour old information. Also, knowing how he abandoned his first child makes me feel disgusted. Last night, he spoke about her as “a mistake” and “a dark secret”. He was never going to tell us about her existence bc he was embarrassed.

Regardless of what happened between he and I, there is a teenager out there who shares 25% of her genetic material with my beautiful children. I don't want that child, who did not ask to be born into such a messy situation, to be separated from her family forever. Even if he does not want to see her, I'd like my kids to eventually know their half sister, bc she deserves to be loved and supported, even if her father cannot.

So now I'm left with options and questions, and I don't know how to proceed. Do I start the process to end my marriage, or do I try to keep my family together? When do we tell our small children about their half sister? Anyone who has experienced this, all advice is welcome.