What should I do after husband had online affair?

My husband is deployed overseas. Him and I have been married 8 years. We have had our issues but we have definitely worked past them and moved on and have been in a fantastic relationship since. He had an online affair once before while he was gone. It was about 3 years ago. He was coming home a few days later so once he got here we both figured out that we wanted to work on our marriage and go from there. We did. We have been absolutely amazing since then, in a point I thought it actually made us stronger. Well, coming to now. A couple weeks ago I had gotten on one of our electronic devices in the house to pull up my social media account. Well, he was still logged in on that and I was about to sign him out and me sign in when I saw a womans name pop up in the messaging system and I thought it was weird because I had never heard the name before. So I clicked on it. I was mortified. Here he is doing it all over again. Mind you this is right after in the same day that he was saying how in love with me he is and that he is so thankful that I have waited for him through so many deployments faithfully and always stuck by his side even when I didn't have to. Well, in the messages they had just started talking that day. I figured that out reading them. And going more in depth she is about 10+ years older then him (the one he talked to 3 years ago was nearly 15+ years older) and this current woman is married to a very wealthy man. She mentioned in the messages that she is very much married and that she would only talk to married men. She said all she wanted was a boyfriend, and then it all started. She sent my husband explicit pictures and asked some from him. Well, he sent them. The messages were awful. To the point I wanted to throw up. The man whom I have spent 10 years with is killing me all over again. Well, I confronted him asking who she was and he said "no one baby" by then he knew I had to have known and he went to work for the night. (since he is overseas their time is way off from ours) But the next day he messaged me saying he had time to think and that he loves me so very much and he just can't keep hurting me over and over again. He said he doesn't know whats wrong with him but he doesn't think he can change. Well, he changed before so I thought. Which was 3 years ago. He could change if he wanted too I believe. I told him we could go to counseling and what not and he expressed nothing was wrong with him but he doesn't know why he keeps doing this over and over again because he loves me and is very happy with me. I'm not sure if its out of boredom or what (he also has a few issues with PTSD) But coming to now. She has blocked me and my family on social media accounts along with my family. She has also blocked us from her husbands facebook, I'm assuming so I had no way to contact him. But believe me there are ways. But I'm not in that position right now to do that because I believe karma will come and bite her. Because she had also mentioned that she does this with other men too. Well, in the messages it was down that she had my work schedule and that they were planning on meeting up while I was at work in a few months when he comes home for a few days. She said she was living in the same state we have a house in. Come to find out she doesn't. She is a state away. I know he is coming home in a few months. Well, not sure if he is coming here or going somewhere else once he gets back stateside. He told me that if he was here he would have never done it. Which I completely agreed. He just isn't that type of person. He just does it when he is away which is odd to me. I have no clue what is going on within his head. I sure wish I knew. We agreed that we would do separation papers as that would save me in the event we do get a divorce. I don't know what will happen when he comes home in a few months. I know they haven't met yet. I understand that. They are just having an online affair and call each other and what not. I have taken a much needed break from social media and everything to try to figure out myself. He has tried contacting me to see where I am and whats going on but I have not replied. I figured the distance would be good for the both of us. I honestly want our relationship to work out. But he has to be willing to change and as of right now he said he can't. I know he is still talking to her, just don't know the extent of it anymore obviously. I'm unsure of what will happen in a few short months. I am so very nervous. I don't know if when he sees me and his daughter he is going to be like what the heck did I do. Or what. Who knows, I keep saying I don't think he will drive a state away to meet up with her once he is here because I know him. But honestly I don't know what I know anymore. I am trying to do things to better myself for me. I just would love to see us work out, but I am stopping the whole I need him thing, more of a want. Just curious if anyone else has been in a similar situation and if you could give me any advice at all. I would greatly appreciate anything given.