Just diagnosed and found my husbands been cheating… now what?

Recently having been diagnosed with stage one cancer I found out the day after my My diagnostic ultrasound that indicated I needed to go for a biopsy and ultimately to my diagnosis, my husband had somebody who had shown an interest in him and he liked it, So after thinking about it I went to him and asked if he would be willing to work on our relationship that I really loved him and wanted to keep it going and myself and our teenage son would really need him during this time I don’t want my son to be my caregiver and I don’t really have any support system other than him and he agreed. I said I was willing to to move forward and do my best to be much better partner wife and anything I could do to make it better for him but I would ask that he would at least stop seeing and talking to this person he promised, that he had not had sex with them. My stress levels I started to rise I started seeing a counsellor which helped, started thinking about what this would mean to me if I got through my treatments but all the while it seems he carried on behind my back. He was kinder and we were having a much more physical relationship, he was being kind sometimes and mean other times, he was always having to run out somewhere and do some thing for some thing, constantly going into the bathroom with his phone, he changed his passwords and all of that prior which is what I had tipped me off in the beginning, so I started to do a little digging myself and came across some really horrifying photographs that I wish I had never seen and ultimately a couple of days of texts that prove to me that he was lying to my face sleeping in my bed and carrying on with this woman. So I confronted him told him that I loved him I did not want to hurt him told him that I understood the reasons why he may have turned to someone else and that I hoped he could love me enough to stay with me through my treatments and support me and my son and not leave my son to be my caregiver and he said that he loved me that he always loved me and he liked this other woman and he didn’t want to stop, saying he said he was sorry, but he didn’t know what to do that he had no thoughts of a plan or what all this with mean. No tears only from me. I asked him if he thought it through if he wanted this to be, I had become aware that she had told her husband and from what I can gather they were making plans together but he said no that there was no plan for him, and I kind of believe he just thought he could carry on with both of us. So once again I’ve asked him can he please wait stop having sex with her stay with me through my upcoming surgery in 15 days and through September when we hope to get our son off to college and out of my house so he’s not in the position of having to go through this with me and that point if my husband would like to go with this other woman I would not stop him and he agreed and we had a nice rest of our day and we acted like it was normal and he hugged me and he told me he loved me and then he went off to work for a week where this woman would be and where previously I know they had been sharing a room. He said it’s all going to be fine he said he’ll be back at the end of the week but in my heart as much as I want to believe it I know that he does not want to give her up he probably is not giving her up he told me he told her I have breast cancer but I don’t think he has and I think they’re just trying to wait out me either getting better or dying but still continuing to have a relationship behind my back and I don’t know what to do. The stress is overwhelming I’m barely able to eat I’m on a regime of wonderful things from my naturopath trying and prepare myself a surgery and for the best outcome, and I can barely keep them down I’m panicked having sort of panic attacks and I want to know how bad is living like this impacting my disease how much will this impact my recovery how much will this cause this thing to grow and spread because I’m not concentrating on healing I’m concentrating on my stress? I do love him but I’ll never trust him again because I know he can lie straight to my face I know he can be with another woman and then be with me in the same day and not feel any remorse and guilt. I truly believe he’s just feeling like the luckiest guy alive getting away with it and the only thing that’s sort of put a wrench in it for him was My diagnosis. I can’t decide what would be best for me, while he’s gone should I pack up his stuff or should I do as I said I would do trust him and work on our marriage even though I know he’s lying, he’s already talking to her in a way I know that they are feeling sorry for each other, and no no sympathy for me of course, which is fair enough I guess they’re feeling sorry that they can’t have their way. I’m just the bad guy I guess again. I dont know what to do.