Update #2: She reached out to me because she was mad my husband stopped talking to her. She thought they would be together but my husband told her no that he loves me and wants to stay in our marriage. She threatened him for a few weeks about telling me just so he will answer her calls and messages. He said he tried distancing himself shortly after this began but she threatened him and he said he didn't want me to leave. I am so beyond torn on what to do. I'm so embarrassed and worried to ask my OB for a STI Check. I'm so angry right now with him. I don't know if I could stay with him but I keep thinking of all the plans I had for us with our child. 

Thank you everyone for your kind words and support. Has meant a lot during this time. I haven't told anyone yet. 

*****Update 3*****: So to answer some questions. He is acting completely different this time. He has broken down several times and keeps saying he will get help and do counseling. He says he knows this time was different. He said he has taken full blame and said he knows its all his fault and isn't blaming her for the blackmailing but that's why it didn't end months ago. I did speak to the woman and she did say he was just trying to keep her happy in the end so she wouldn't do it but she had to send it. I'm not blaming her because my husband is the one to blame but she knew my husband was married. She saw him at work and then two months later asked a coworker for his number. They both confirmed that story. She was emailing me constantly sending me messages between them. I don't want to see this anymore. I told her on the phone when we talked that I don't need the details but she keeps doing it anyway. She also keeps reminding me how he ruined my pregnancy and I said he didn't ruin anything. I love my baby so much and I want her. She stumbled and said no not like that like forever every time you think of this pregnancy you will think of this and when you look at your baby you will think of everything. I told her no that's not true. Then she messaged me again and sent a bulleted email as to why I shouldnt stay with my husband. She isn't a nice person. I know someone said that. She won't stop sending things. She's trying to hurt me and ensure I leave him. I am clearly already hurt so why keep digging. She knows I'm pregnant and I've told her that this isn't good for my baby. I think she wants to be with him that's why.  He said he will do all the work this time because I said I do not want to go through this again. It was bad the first time. He said he will call me constantly, text, and said he would quit his job so he has different hours. He said he will even install cameras in the house so I can see if he leaves or anyone is there. I said that's a little crazy and he said he will do it. He said he will print the phone bill out every night so I can see who he has called or texted. He also told me he will tell me when he talks to any girl like for work. Which I know can be a line.  He is begging me. He said its different because of what he's losing now. I said I don't want to do anything while I'm pregnant because I will not do this to my baby. So we are separating until the baby comes and re-evaluate the situation after she's born. I am so lost and in a sea of emotions. I don't know what to believe with him. Thank you everyone for your support and kind words. I haven't talked to anyone else so reading your messages helps me through the night sometimes. 

****Update 4****: So to update some people and give some background. We have started counseling but not to stay together just to help talk and even see if this is worth saving. I said I didn't want to do this while pregnant but I've been struggling badly. I am worried for my child. Today was the first day that I actually got some rest since everything. I've lost weight. Some background to me and my husband. We have been together for 17 years. We have been through everything together. It's hard to walk away from that. Even if we don't stay together, we still have to be in each other's lives and he is truly my best friend. He wasn't always like this so I didn't marry a cheater like someone asked if I did. I know where this comes from. He struggled with something I rather not get into and our marriage suffered for it. I blame him for what he has done 100%. I'm not stupid nor do I excuse what he did but I will take some part in why everything changed between us. It wasn't always like this. He shut down so I got angry. We did fight a lot and I didn't always speak to him kindly. I struggled with how to get him back. He never cared to admit he had an issue but after this, he said he does need help and I plan to seek a counselor individually to help me through this. He has been very remorseful and been there for me. In a total of the past week, he hasn't gotten any sleep really. He's missing work (which he loves a lot). He stays up all night talking to me. If he isn't truly remorseful then he's a damn good actor. So far he's been doing what's right but I said no to us staying together until I see this change permanently. I still am unsure what to do. I feel like I need time and soon enough it will be clearer for me. I don't want to be played a fool either so I want to make sure he's genuine because I will not go through this a second time and he knows that. I said I don't want to expose our child to this. 

Also pertaining to the affair, it wasn't a consistent one year relationship. They met a total of 10 times over the year. Not saying that makes it any better. He stopped it when we started trying to get pregnant when our marriage was going back on track and she reached out to him several times during this. He didn't answer and she started to threaten him and he got scared because I was pregnant and he didn't want to lose me or have me experience this heartbreak pregnant. He begged her to wait to tell me until the pregnancy was over so I didn't go through this pregnant. He said he would tell me right after but she said no she needs to do it now and he said what's the point. She said she needed it. So not saying it makes it any better. There was no relationship where they like hung out or went out to eat or bought gifts or anything like that. Both have confirmed this although she wants it to be. I have not spoken to her since the last time last week. She told some of this in one of her emails. I haven't had contact with her after telling her to stop contacting me. It still hurts that he did that for so long and I can't even look at him sometimes. Thank you everyone again for the advice. Much appreciated. 

****Add on**** I just wanted to add that I am reading each and every post on here and the outpouring of support and kind words during this time has helped me more than I can express. Thank you to everyone who has called me strong. I do have to say I don't feel that strong. I had several breaks down like really bad and I would cramp. It scared me so much and made me realize that right now that isn't helping. I need to take care of my baby. She is everything to me. She truly has changed me into a better person since I found out she was here. I have my moments still but I figured the counselor will help me through it and help where they won't get so bad. I still question everything and have been on a roller coaster since day one. All of your posts whether it's to stay or go, have helped. I need to wait to make a decision permanently. This isn't just about me. I also wanted to say I am so sorry for all the women on here who said they have gone through this too!! Sending all of you prayers and support as well.