My husband's mistress contacted me. She's pregnant.

Basically the title. My husband (M 52) and I (40) haven't been living together since November. I have been living with my parents as I am at the moment their sole care taker after the hired help that we had before got sick with COVID. My husband didn't have the choice to stay home and work so we felt it would be better if I lived with my parents to reduce chance of exposure. So we haven't had sex since then basically and our conversations have been over the phone, through the door screen when he drops off groceries and on zoom. Until a few days ago, I had no idea he was having an affair.

A new temp secretary was hired in October and I guess my husband had been flirting with her without much shame. According to her, she had no idea he was married and he wasn't even wearing his wedding ring at work. They started having sex at work in secret. Mid November, ( which would have been about two weeks after I moved into my parent's home,) he invited her over. They had sex and she has been staying in my home with my husband on and off. She found out she was pregnant on Christmas and they celebrated. She had no idea I existed until she found photos of me, him and our child hidden in a drawer. That's when she did some research and found out about me. She messaged me on FB and told me all this in a long message, pratically detailing every encounter. As well as pictures.

She told me she would of left if she wasn't pregnant but she wants this family with him. She's 26 and so pretty. I can't compete with that.

I don't know what to do. I haven't confronted my husband yet and I have no clue if knows that I know. He could be waiting for me to call or he could be as clueless as I was. I'm just so shocked. I don't know where to start or what to do. Our son lives in another state and he'll be crushed to hear this. Do I just let her have him? Our son is adopted and I know he's always wanted bio children. Please help with any advice.

Update text:

I'd like to start by saying I appreciated all the feedback and advice given. I walked away from the post for a couple of hours and it was locked before I could respond, but I did read all of the comments. So thank you.

A lot has happened since the post. First off I'm getting a divorce. I am legally separated from my husband for now and I am in the process of filing for divorce. I confronted him pretty quickly and he came clean, telling me it was a mistake and just wanted to feel young again. All the BS. He didn't mean for it to get this far but he fell in love because she reminded him of me when I was younger.

He said he still loves me and is willing to kick her out and he'd move in with me and my parents. I said no. He's got a kid on the way and I want nothing to do with it. Our son is on my side and is no longer speaking to my husband.

I guess this part is the karma. He broke up with her and kicked her out, she's now made a complaint to his work's HR for sexual harrassment and is suing him. So that's happening as well.

I'm still heart broken but relieved I'm not alone. My parents are so supportive, my son has been amazing. I'm just grateful for the support.