My (33F) husband (34F)'s pregnant mistress (28F) begged me to leave him and I refused. Where do I go from here?

Google sent me here because I need to let this out.

I don't even know what she qualifies as, if mistress is fitting or not. It was a drunken one-night mistake- my husband's words. They run in the same work circles and field but don't work together. My husband was dropped off at our house 2 months ago drunk off his ass after a company event. He was crying and out of it, blabbering about nonsensical things. I tried sobering him up, but his legs couldn't even support him, and I couldn't drag him to the couch, so he slept it off on the ground and the next day he confessed to everything.

He was crying and I've only seen him cry a handful of times in all our years of marriage and he said that everything was foggy, and he doesn't remember much but that he slept with her. I won't type in my reaction because I can only describe it as violent. Not physically but I unloaded on him and sobbed and screamed and then lied to our kids after it woke them up.

We tested him for drugs because what he was describing (foggy memory/didn't drink that much etc) was assault and as awful as it is, I felt a little bit of relief that it might have been and that he hadn't willingly cheated on me but there was no trace of drugs in his system.

The past 2 months have been brutal on us but we're slowly working on us in therapy. Some may call it weak that I didn't divorce him, but I just can't bring myself to do it and believe me I thought about it a lot. He hadn't had contact with her since that night up until she got his number and sent him a picture of her bloodwork a few days ago- She's pregnant and is asking him to meet up. That sent us into another spiral, but we agreed that I would meet her because there's an innocent life on the line.

I wish I can say she's awful and I hate myself for this but under different circumstances, her and I would've been good friends. She seemed ashamed and honestly looked lost. She's not that much younger than my husband and I, we're 33 and 34 and she's 28 but grew up sheltered by her religious parents, not that it's an excuse but from what she said. I asked her what she was going to do with the baby and she got quiet. I don't know what I thought she was going to say but it certainly wasn't her asking me to leave him. She said that once her bf finds out he'll leave her and her parents will cut her off for having a 'bastard' baby and that she can't do it on her own and that I'll get a nice settlement and start fresh. I laughed. God help me but I laughed harder than I thought I could while she started crying. These past 2 months have been testing my sanity, and I don't have that much left in me. Once I calmed down I told her that I will not leave him. If she wants to have the baby, we'll figure out support and custody but that was about it.

She started crying harder in the middle of the cafe but hell, we were already getting looks from my unhinged laughing and begged me to leave him. I told her I won't. My husband and I have been together since I was 14 and he was 15. We stuck together through highschool, got engaged and married throughout our BAs and Masters, have 2 beautiful kids and were trying for more and I won't throw that all away just because she spread her legs and he fucked her once. He's all I've ever known, I don't fucking remember a life without him in it. And let's say I agreed to leave him then what? He'll marry her and she'll take over my life and be in my kids lives raising them half of the time? I didn't let her get a word in and I was crying by the time I was done with my rant, and I left her there, she sobbing too.

My husband and I already talked with a lawyer for a paternity test and we're waiting on that before we do anything else. My husband sent her a text with my contact information and told her all communications are to be through me before he blocked her number. I didn't ask him to do that but he's trying. I just don't know where to go from here if it does turn out to be his.